diff --git a/modules/openapi-generator/src/main/resources/typescript/configuration.mustache b/modules/openapi-generator/src/main/resources/typescript/configuration.mustache
index e16f368d889..06fb3994de6 100644
--- a/modules/openapi-generator/src/main/resources/typescript/configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript/configuration.mustache
@@ -12,16 +12,16 @@ import { BaseServerConfiguration, server1 } from "./servers{{importFileExtension
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth{{importFileExtension}}";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -105,43 +105,36 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  */
 {{#useInversify}}
 export function mergeConfiguration(conf: Configuration, options?: Configuration): Configuration {
-    if (options) {
-        conf = options;
-    }
-    return conf;
+    return options || conf;
 }
 {{/useInversify}}
 {{^useInversify}}
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 {{/useInversify}}
 
diff --git a/modules/openapi-generator/src/main/resources/typescript/types/ObservableAPI.mustache b/modules/openapi-generator/src/main/resources/typescript/types/ObservableAPI.mustache
index f7a2c71014f..f1eab3a96ba 100644
--- a/modules/openapi-generator/src/main/resources/typescript/types/ObservableAPI.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript/types/ObservableAPI.mustache
@@ -65,14 +65,14 @@ export class Observable{{classname}} {
     public {{nickname}}WithHttpInfo({{#allParams}}{{paramName}}{{^required}}?{{/required}}: {{{dataType}}}, {{/allParams}}_options?: Configuration{{^useInversify}}Options{{/useInversify}}): Observable<HttpInfo<{{{returnType}}}{{^returnType}}void{{/returnType}}>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.{{nickname}}({{#allParams}}{{paramName}}, {{/allParams}}{{#useInversify}}_options{{/useInversify}}{{^useInversify}}_config{{/useInversify}});
+        const requestContextPromise = this.requestFactory.{{nickname}}({{#allParams}}{{paramName}}, {{/allParams}}_config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/client/echo_api/typescript/build/configuration.ts b/samples/client/echo_api/typescript/build/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/echo_api/typescript/build/configuration.ts
+++ b/samples/client/echo_api/typescript/build/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/echo_api/typescript/build/types/ObservableAPI.ts b/samples/client/echo_api/typescript/build/types/ObservableAPI.ts
index 2032d741f30..ebedfaf274d 100644
--- a/samples/client/echo_api/typescript/build/types/ObservableAPI.ts
+++ b/samples/client/echo_api/typescript/build/types/ObservableAPI.ts
@@ -46,7 +46,7 @@ export class ObservableAuthApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -78,7 +78,7 @@ export class ObservableAuthApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -128,7 +128,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -161,7 +161,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -195,7 +195,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -229,7 +229,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -263,7 +263,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -297,7 +297,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -331,7 +331,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -365,7 +365,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -399,7 +399,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -433,7 +433,7 @@ export class ObservableBodyApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -487,7 +487,7 @@ export class ObservableFormApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -523,7 +523,7 @@ export class ObservableFormApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -562,7 +562,7 @@ export class ObservableFormApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -623,7 +623,7 @@ export class ObservableHeaderApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -682,7 +682,7 @@ export class ObservablePathApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -738,7 +738,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -775,7 +775,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -813,7 +813,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -849,7 +849,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -883,7 +883,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -917,7 +917,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -951,7 +951,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -985,7 +985,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1019,7 +1019,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1053,7 +1053,7 @@ export class ObservableQueryApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/client/others/typescript/builds/array-of-lists/configuration.ts b/samples/client/others/typescript/builds/array-of-lists/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/others/typescript/builds/array-of-lists/configuration.ts
+++ b/samples/client/others/typescript/builds/array-of-lists/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/others/typescript/builds/array-of-lists/types/ObservableAPI.ts b/samples/client/others/typescript/builds/array-of-lists/types/ObservableAPI.ts
index c81c9ff213d..5a77711dfea 100644
--- a/samples/client/others/typescript/builds/array-of-lists/types/ObservableAPI.ts
+++ b/samples/client/others/typescript/builds/array-of-lists/types/ObservableAPI.ts
@@ -34,7 +34,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/client/others/typescript/builds/enum-single-value/configuration.ts b/samples/client/others/typescript/builds/enum-single-value/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/others/typescript/builds/enum-single-value/configuration.ts
+++ b/samples/client/others/typescript/builds/enum-single-value/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/others/typescript/builds/null-types-simple/configuration.ts b/samples/client/others/typescript/builds/null-types-simple/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/others/typescript/builds/null-types-simple/configuration.ts
+++ b/samples/client/others/typescript/builds/null-types-simple/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/others/typescript/builds/with-unique-items/configuration.ts b/samples/client/others/typescript/builds/with-unique-items/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/others/typescript/builds/with-unique-items/configuration.ts
+++ b/samples/client/others/typescript/builds/with-unique-items/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/others/typescript/builds/with-unique-items/types/ObservableAPI.ts b/samples/client/others/typescript/builds/with-unique-items/types/ObservableAPI.ts
index 54132586b76..8c4dae1fb56 100644
--- a/samples/client/others/typescript/builds/with-unique-items/types/ObservableAPI.ts
+++ b/samples/client/others/typescript/builds/with-unique-items/types/ObservableAPI.ts
@@ -33,7 +33,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/client/others/typescript/encode-decode/build/configuration.ts b/samples/client/others/typescript/encode-decode/build/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/client/others/typescript/encode-decode/build/configuration.ts
+++ b/samples/client/others/typescript/encode-decode/build/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/client/others/typescript/encode-decode/build/types/ObservableAPI.ts b/samples/client/others/typescript/encode-decode/build/types/ObservableAPI.ts
index e4b2aa862ec..98a4d0cbf06 100644
--- a/samples/client/others/typescript/encode-decode/build/types/ObservableAPI.ts
+++ b/samples/client/others/typescript/encode-decode/build/types/ObservableAPI.ts
@@ -34,7 +34,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -62,7 +62,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -90,7 +90,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -118,7 +118,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -146,7 +146,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -174,7 +174,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -202,7 +202,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -230,7 +230,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -258,7 +258,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -286,7 +286,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -314,7 +314,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -342,7 +342,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -370,7 +370,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -398,7 +398,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -426,7 +426,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -454,7 +454,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -483,7 +483,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -513,7 +513,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -543,7 +543,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -573,7 +573,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -603,7 +603,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -633,7 +633,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -663,7 +663,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -693,7 +693,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -723,7 +723,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -753,7 +753,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -783,7 +783,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -813,7 +813,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -843,7 +843,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -873,7 +873,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -903,7 +903,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -933,7 +933,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/browser/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/browser/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/browser/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/browser/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/browser/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/browser/types/ObservableAPI.ts
index 58459af26d4..0ccd300d0fc 100644
--- a/samples/openapi3/client/petstore/typescript/builds/browser/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/browser/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/types/ObservableAPI.ts
index 5cfef19528d..3f657b1f314 100644
--- a/samples/openapi3/client/petstore/typescript/builds/composed-schemas/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/composed-schemas/types/ObservableAPI.ts
@@ -40,7 +40,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -70,7 +70,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -100,7 +100,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/default/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/default/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/default/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/default/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/default/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/default/types/ObservableAPI.ts
index 58459af26d4..0ccd300d0fc 100644
--- a/samples/openapi3/client/petstore/typescript/builds/default/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/default/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/deno/configuration.ts
index 1996d770eb1..2869965cf9c 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers.ts";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth.ts";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/deno/types/ObservableAPI.ts
index e2bc011b234..6a38fcfe63d 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/configuration.ts
index 1996d770eb1..2869965cf9c 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers.ts";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth.ts";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/types/ObservableAPI.ts
index e2bc011b234..6a38fcfe63d 100644
--- a/samples/openapi3/client/petstore/typescript/builds/deno_object_params/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/deno_object_params/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/explode-query/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/explode-query/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/explode-query/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/explode-query/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/explode-query/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/explode-query/types/ObservableAPI.ts
index 7e20b920403..e6627dbbe7a 100644
--- a/samples/openapi3/client/petstore/typescript/builds/explode-query/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/explode-query/types/ObservableAPI.ts
@@ -82,7 +82,7 @@ export class ObservableAnotherFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -131,7 +131,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -178,7 +178,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -208,7 +208,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -241,7 +241,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -275,7 +275,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -307,7 +307,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -339,7 +339,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -371,7 +371,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -403,7 +403,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -435,7 +435,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -467,7 +467,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -499,7 +499,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -532,7 +532,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -579,7 +579,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -634,7 +634,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -681,7 +681,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -720,7 +720,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -755,7 +755,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -795,7 +795,7 @@ export class ObservableFakeApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -852,7 +852,7 @@ export class ObservableFakeClassnameTags123Api {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -904,7 +904,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -939,7 +939,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -974,7 +974,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1008,7 +1008,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1042,7 +1042,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1076,7 +1076,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1112,7 +1112,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1150,7 +1150,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1188,7 +1188,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1242,7 +1242,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1275,7 +1275,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1308,7 +1308,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1342,7 +1342,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1394,7 +1394,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1428,7 +1428,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1462,7 +1462,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1496,7 +1496,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1530,7 +1530,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1565,7 +1565,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1599,7 +1599,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -1633,7 +1633,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/inversify/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/inversify/configuration.ts
index 586313ff22e..7f1fad5c3e1 100644
--- a/samples/openapi3/client/petstore/typescript/builds/inversify/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/inversify/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,10 +97,7 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: Configuration): Configuration {
-    if (options) {
-        conf = options;
-    }
-    return conf;
+    return options || conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/inversify/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/inversify/types/ObservableAPI.ts
index 85b1058c73a..9317ecb7bef 100644
--- a/samples/openapi3/client/petstore/typescript/builds/inversify/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/inversify/types/ObservableAPI.ts
@@ -39,14 +39,14 @@ export class ObservablePetApi {
     public addPetWithHttpInfo(pet: Pet, _options?: Configuration): Observable<HttpInfo<Pet>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.addPet(pet, _options);
+        const requestContextPromise = this.requestFactory.addPet(pet, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -74,14 +74,14 @@ export class ObservablePetApi {
     public deletePetWithHttpInfo(petId: number, apiKey?: string, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.deletePet(petId, apiKey, _options);
+        const requestContextPromise = this.requestFactory.deletePet(petId, apiKey, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -109,14 +109,14 @@ export class ObservablePetApi {
     public findPetsByStatusWithHttpInfo(status: Array<'available' | 'pending' | 'sold'>, _options?: Configuration): Observable<HttpInfo<Array<Pet>>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.findPetsByStatus(status, _options);
+        const requestContextPromise = this.requestFactory.findPetsByStatus(status, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -143,14 +143,14 @@ export class ObservablePetApi {
     public findPetsByTagsWithHttpInfo(tags: Array<string>, _options?: Configuration): Observable<HttpInfo<Array<Pet>>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.findPetsByTags(tags, _options);
+        const requestContextPromise = this.requestFactory.findPetsByTags(tags, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -177,14 +177,14 @@ export class ObservablePetApi {
     public getPetByIdWithHttpInfo(petId: number, _options?: Configuration): Observable<HttpInfo<Pet>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.getPetById(petId, _options);
+        const requestContextPromise = this.requestFactory.getPetById(petId, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -211,14 +211,14 @@ export class ObservablePetApi {
     public updatePetWithHttpInfo(pet: Pet, _options?: Configuration): Observable<HttpInfo<Pet>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.updatePet(pet, _options);
+        const requestContextPromise = this.requestFactory.updatePet(pet, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -247,14 +247,14 @@ export class ObservablePetApi {
     public updatePetWithFormWithHttpInfo(petId: number, name?: string, status?: string, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.updatePetWithForm(petId, name, status, _options);
+        const requestContextPromise = this.requestFactory.updatePetWithForm(petId, name, status, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -285,14 +285,14 @@ export class ObservablePetApi {
     public uploadFileWithHttpInfo(petId: number, additionalMetadata?: string, file?: HttpFile, _options?: Configuration): Observable<HttpInfo<ApiResponse>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.uploadFile(petId, additionalMetadata, file, _options);
+        const requestContextPromise = this.requestFactory.uploadFile(petId, additionalMetadata, file, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -342,14 +342,14 @@ export class ObservableStoreApi {
     public deleteOrderWithHttpInfo(orderId: string, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.deleteOrder(orderId, _options);
+        const requestContextPromise = this.requestFactory.deleteOrder(orderId, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -375,14 +375,14 @@ export class ObservableStoreApi {
     public getInventoryWithHttpInfo(_options?: Configuration): Observable<HttpInfo<{ [key: string]: number; }>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.getInventory(_options);
+        const requestContextPromise = this.requestFactory.getInventory(_config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -408,14 +408,14 @@ export class ObservableStoreApi {
     public getOrderByIdWithHttpInfo(orderId: number, _options?: Configuration): Observable<HttpInfo<Order>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.getOrderById(orderId, _options);
+        const requestContextPromise = this.requestFactory.getOrderById(orderId, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -442,14 +442,14 @@ export class ObservableStoreApi {
     public placeOrderWithHttpInfo(order: Order, _options?: Configuration): Observable<HttpInfo<Order>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.placeOrder(order, _options);
+        const requestContextPromise = this.requestFactory.placeOrder(order, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -497,14 +497,14 @@ export class ObservableUserApi {
     public createUserWithHttpInfo(user: User, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.createUser(user, _options);
+        const requestContextPromise = this.requestFactory.createUser(user, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -531,14 +531,14 @@ export class ObservableUserApi {
     public createUsersWithArrayInputWithHttpInfo(user: Array<User>, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.createUsersWithArrayInput(user, _options);
+        const requestContextPromise = this.requestFactory.createUsersWithArrayInput(user, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -565,14 +565,14 @@ export class ObservableUserApi {
     public createUsersWithListInputWithHttpInfo(user: Array<User>, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.createUsersWithListInput(user, _options);
+        const requestContextPromise = this.requestFactory.createUsersWithListInput(user, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -599,14 +599,14 @@ export class ObservableUserApi {
     public deleteUserWithHttpInfo(username: string, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.deleteUser(username, _options);
+        const requestContextPromise = this.requestFactory.deleteUser(username, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -633,14 +633,14 @@ export class ObservableUserApi {
     public getUserByNameWithHttpInfo(username: string, _options?: Configuration): Observable<HttpInfo<User>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.getUserByName(username, _options);
+        const requestContextPromise = this.requestFactory.getUserByName(username, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -668,14 +668,14 @@ export class ObservableUserApi {
     public loginUserWithHttpInfo(username: string, password: string, _options?: Configuration): Observable<HttpInfo<string>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.loginUser(username, password, _options);
+        const requestContextPromise = this.requestFactory.loginUser(username, password, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -702,14 +702,14 @@ export class ObservableUserApi {
     public logoutUserWithHttpInfo(_options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.logoutUser(_options);
+        const requestContextPromise = this.requestFactory.logoutUser(_config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -736,14 +736,14 @@ export class ObservableUserApi {
     public updateUserWithHttpInfo(username: string, user: User, _options?: Configuration): Observable<HttpInfo<void>> {
         const _config = mergeConfiguration(this.configuration, _options);
 
-        const requestContextPromise = this.requestFactory.updateUser(username, user, _options);
+        const requestContextPromise = this.requestFactory.updateUser(username, user, _config);
         // build promise chain
         let middlewarePreObservable = from<RequestContext>(requestContextPromise);
         for (const middleware of _config.middleware) {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/jquery/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/jquery/configuration.ts
index ed54d874a86..85521458d94 100644
--- a/samples/openapi3/client/petstore/typescript/builds/jquery/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/jquery/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/jquery/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/jquery/types/ObservableAPI.ts
index 58459af26d4..0ccd300d0fc 100644
--- a/samples/openapi3/client/petstore/typescript/builds/jquery/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/jquery/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/types/ObservableAPI.ts
index 54132586b76..8c4dae1fb56 100644
--- a/samples/openapi3/client/petstore/typescript/builds/nullable-enum/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/nullable-enum/types/ObservableAPI.ts
@@ -33,7 +33,7 @@ export class ObservableDefaultApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/builds/object_params/configuration.ts b/samples/openapi3/client/petstore/typescript/builds/object_params/configuration.ts
index 483dc5e5413..4e654728905 100644
--- a/samples/openapi3/client/petstore/typescript/builds/object_params/configuration.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/object_params/configuration.ts
@@ -5,16 +5,16 @@ import { BaseServerConfiguration, server1 } from "./servers";
 import { configureAuthMethods, AuthMethods, AuthMethodsConfiguration } from "./auth/auth";
 
 export interface Configuration<M = Middleware> {
-  readonly baseServer: BaseServerConfiguration;
-  readonly httpApi: HttpLibrary;
-  readonly middleware: M[];
-  readonly authMethods: AuthMethods;
+    readonly baseServer: BaseServerConfiguration;
+    readonly httpApi: HttpLibrary;
+    readonly middleware: M[];
+    readonly authMethods: AuthMethods;
 }
 
 // Additional option specific to middleware merge strategy
 export interface MiddlewareMergeOptions {
-  // default is `'replace'` for backwards compatibility
-  middlewareMergeStrategy?: 'replace' | 'append' | 'prepend';
+    // default is `"replace"` for backwards compatibility
+    middlewareMergeStrategy?: "replace" | "append" | "prepend";
 }
 
 // Unify configuration options using Partial plus extra merge strategy
@@ -97,35 +97,31 @@ export function createConfiguration(conf: ConfigurationParameters = {}): Configu
  * Merge configuration options into a configuration.
  */
 export function mergeConfiguration(conf: Configuration, options?: ConfigurationOptions): Configuration {
-    let allMiddleware: Middleware[] = [];
-    if (options && options.middleware) {
-        const middlewareMergeStrategy = options.middlewareMergeStrategy || "replace" // default to replace behavior
-        // call-time middleware provided
-        const calltimeMiddleware: Middleware[] = options.middleware;
+    if (!options) {
+        return conf;
+    }
+    return {
+        baseServer: options.baseServer || conf.baseServer,
+        httpApi: options.httpApi || conf.httpApi,
+        authMethods: options.authMethods || conf.authMethods,
+        middleware: mergeMiddleware(conf.middleware, options?.middleware, options?.middlewareMergeStrategy),
+    };
+}
 
-        switch(middlewareMergeStrategy) {
+function mergeMiddleware(staticMiddleware: Middleware[], calltimeMiddleware?: Middleware[], strategy: "append" | "prepend" | "replace" = "replace") {
+    if (!calltimeMiddleware) {
+        return staticMiddleware;
+    }
+    switch(strategy) {
         case "append":
-            allMiddleware = conf.middleware.concat(calltimeMiddleware);
-            break;
+            return staticMiddleware.concat(calltimeMiddleware);
         case "prepend":
-            allMiddleware = calltimeMiddleware.concat(conf.middleware)
-            break;
+            return calltimeMiddleware.concat(staticMiddleware)
         case "replace":
-            allMiddleware = calltimeMiddleware
-            break;
+            return calltimeMiddleware
         default:
-            throw new Error(`unrecognized middleware merge strategy '${middlewareMergeStrategy}'`);
-        }
+            throw new Error(`Unrecognized middleware merge strategy '${strategy}'`)
     }
-    if (options) {
-        conf = {
-          baseServer: options.baseServer || conf.baseServer,
-          httpApi: options.httpApi || conf.httpApi,
-          authMethods: options.authMethods || conf.authMethods,
-          middleware: allMiddleware || conf.middleware
-        };
-    }
-    return conf;
 }
 
 /**
diff --git a/samples/openapi3/client/petstore/typescript/builds/object_params/types/ObservableAPI.ts b/samples/openapi3/client/petstore/typescript/builds/object_params/types/ObservableAPI.ts
index 58459af26d4..0ccd300d0fc 100644
--- a/samples/openapi3/client/petstore/typescript/builds/object_params/types/ObservableAPI.ts
+++ b/samples/openapi3/client/petstore/typescript/builds/object_params/types/ObservableAPI.ts
@@ -41,7 +41,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -76,7 +76,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -111,7 +111,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -145,7 +145,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -179,7 +179,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -213,7 +213,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -249,7 +249,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -287,7 +287,7 @@ export class ObservablePetApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -341,7 +341,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -374,7 +374,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -407,7 +407,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -441,7 +441,7 @@ export class ObservableStoreApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -493,7 +493,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -527,7 +527,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -561,7 +561,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -595,7 +595,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -629,7 +629,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -664,7 +664,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -698,7 +698,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
@@ -732,7 +732,7 @@ export class ObservableUserApi {
             middlewarePreObservable = middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => middleware.pre(ctx)));
         }
 
-        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => this.configuration.httpApi.send(ctx))).
+        return middlewarePreObservable.pipe(mergeMap((ctx: RequestContext) => _config.httpApi.send(ctx))).
             pipe(mergeMap((response: ResponseContext) => {
                 let middlewarePostObservable = of(response);
                 for (const middleware of _config.middleware.reverse()) {
diff --git a/samples/openapi3/client/petstore/typescript/tests/default/test/api/PetApi.test.ts b/samples/openapi3/client/petstore/typescript/tests/default/test/api/PetApi.test.ts
index ab402abc816..c8137a5312e 100644
--- a/samples/openapi3/client/petstore/typescript/tests/default/test/api/PetApi.test.ts
+++ b/samples/openapi3/client/petstore/typescript/tests/default/test/api/PetApi.test.ts
@@ -1,5 +1,5 @@
 import * as petstore from 'ts-petstore-client'
-import { Middleware, RequestContext, ResponseContext } from 'ts-petstore-client'
+import { Middleware, RequestContext, ResponseContext, wrapHttpLibrary } from 'ts-petstore-client'
 
 import { expect } from "chai";
 import * as fs from 'fs';
@@ -103,6 +103,24 @@ describe("PetApi", () => {
     expect(CallOrder).deep.equal(['base-pre', 'base-post'])
   })
 
+  it("should keep middleware when options are given without middleware", async () => {
+    let { CallOrder, BaseMiddleware, CalltimeMiddleware } = MiddlewareCallTracker()
+    const configuration = petstore.createConfiguration({ promiseMiddleware: [BaseMiddleware] });
+    const petApi = new petstore.PetApi(configuration);
+    const callTimeAppendedRightPet = await petApi.getPetById(pet.id, {});
+    expect(callTimeAppendedRightPet).to.deep.equal(pet);
+    expect(CallOrder).deep.equal(['base-pre', 'base-post'])
+  })
+
+  it("should replace middleware when options contain an empty array of middlewares", async () => {
+    let { CallOrder, BaseMiddleware, CalltimeMiddleware } = MiddlewareCallTracker()
+    const configuration = petstore.createConfiguration({ promiseMiddleware: [BaseMiddleware] });
+    const petApi = new petstore.PetApi(configuration);
+    const callTimeAppendedRightPet = await petApi.getPetById(pet.id, { middleware: [] });
+    expect(callTimeAppendedRightPet).to.deep.equal(pet);
+    expect(CallOrder).deep.equal([])
+  })
+
   it("replace Middleware call order", async () => {
     let { CallOrder, BaseMiddleware, CalltimeMiddleware } = MiddlewareCallTracker()
     const configuration = petstore.createConfiguration({ promiseMiddleware: [BaseMiddleware] })
@@ -140,6 +158,31 @@ describe("PetApi", () => {
     expect(callTimeAppendedRightPet).to.deep.equal(pet);
   })
 
+  it("should override http api from option", async () => {
+    const configuration = petstore.createConfiguration();
+    const petApi = new petstore.PetApi(configuration);
+
+    let overriddenCalls = 0;
+    const mockHttpLibrary = {
+      async send(): Promise<ResponseContext> {
+        overriddenCalls++;
+        return new ResponseContext(200, {
+          "content-type": "application/json",
+        }, {
+          async text() {
+            return "{}";
+          },
+          async binary() {
+            throw new Error("Unexpected usage of mock body as binary.");
+          }
+        });
+      }
+    };
+
+    await petApi.getPetById(pet.id, { httpApi: wrapHttpLibrary(mockHttpLibrary) });
+    expect(overriddenCalls).to.equal(1);
+  })
+
   it("deletePet", async () => {
     await petApi.deletePet(pet.id);
     let deletedPet;