diff --git a/modules/openapi-generator/src/main/resources/typescript-rxjs/runtime.mustache b/modules/openapi-generator/src/main/resources/typescript-rxjs/runtime.mustache
index a978bd7d2cc..366d9b5c441 100644
--- a/modules/openapi-generator/src/main/resources/typescript-rxjs/runtime.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-rxjs/runtime.mustache
@@ -36,12 +36,18 @@ export class Configuration {
 
     get apiKey(): ((name: string) => string) | undefined {
         const apiKey = this.configuration.apiKey;
-        return apiKey && (typeof apiKey === 'function' ? apiKey : () => apiKey);
+        if (!apiKey) {
+            return undefined;
+        }
+        return typeof apiKey === 'string' ? () => apiKey : apiKey;
     }
 
     get accessToken(): ((name: string, scopes?: string[]) => string) | undefined {
         const accessToken = this.configuration.accessToken;
-        return accessToken && (typeof accessToken === 'function' ? accessToken : () => accessToken);
+        if (!accessToken) {
+            return undefined;
+        }
+        return typeof accessToken === 'string' ? () => accessToken : accessToken;
     }
 }
 
diff --git a/samples/client/petstore/typescript-rxjs/builds/default/runtime.ts b/samples/client/petstore/typescript-rxjs/builds/default/runtime.ts
index 40d2e7b3947..e4c93e87e51 100644
--- a/samples/client/petstore/typescript-rxjs/builds/default/runtime.ts
+++ b/samples/client/petstore/typescript-rxjs/builds/default/runtime.ts
@@ -47,12 +47,18 @@ export class Configuration {
 
     get apiKey(): ((name: string) => string) | undefined {
         const apiKey = this.configuration.apiKey;
-        return apiKey && (typeof apiKey === 'function' ? apiKey : () => apiKey);
+        if (!apiKey) {
+            return undefined;
+        }
+        return typeof apiKey === 'string' ? () => apiKey : apiKey;
     }
 
     get accessToken(): ((name: string, scopes?: string[]) => string) | undefined {
         const accessToken = this.configuration.accessToken;
-        return accessToken && (typeof accessToken === 'function' ? accessToken : () => accessToken);
+        if (!accessToken) {
+            return undefined;
+        }
+        return typeof accessToken === 'string' ? () => accessToken : accessToken;
     }
 }
 
diff --git a/samples/client/petstore/typescript-rxjs/builds/es6-target/runtime.ts b/samples/client/petstore/typescript-rxjs/builds/es6-target/runtime.ts
index 40d2e7b3947..e4c93e87e51 100644
--- a/samples/client/petstore/typescript-rxjs/builds/es6-target/runtime.ts
+++ b/samples/client/petstore/typescript-rxjs/builds/es6-target/runtime.ts
@@ -47,12 +47,18 @@ export class Configuration {
 
     get apiKey(): ((name: string) => string) | undefined {
         const apiKey = this.configuration.apiKey;
-        return apiKey && (typeof apiKey === 'function' ? apiKey : () => apiKey);
+        if (!apiKey) {
+            return undefined;
+        }
+        return typeof apiKey === 'string' ? () => apiKey : apiKey;
     }
 
     get accessToken(): ((name: string, scopes?: string[]) => string) | undefined {
         const accessToken = this.configuration.accessToken;
-        return accessToken && (typeof accessToken === 'function' ? accessToken : () => accessToken);
+        if (!accessToken) {
+            return undefined;
+        }
+        return typeof accessToken === 'string' ? () => accessToken : accessToken;
     }
 }
 
diff --git a/samples/client/petstore/typescript-rxjs/builds/with-interfaces/runtime.ts b/samples/client/petstore/typescript-rxjs/builds/with-interfaces/runtime.ts
index 40d2e7b3947..e4c93e87e51 100644
--- a/samples/client/petstore/typescript-rxjs/builds/with-interfaces/runtime.ts
+++ b/samples/client/petstore/typescript-rxjs/builds/with-interfaces/runtime.ts
@@ -47,12 +47,18 @@ export class Configuration {
 
     get apiKey(): ((name: string) => string) | undefined {
         const apiKey = this.configuration.apiKey;
-        return apiKey && (typeof apiKey === 'function' ? apiKey : () => apiKey);
+        if (!apiKey) {
+            return undefined;
+        }
+        return typeof apiKey === 'string' ? () => apiKey : apiKey;
     }
 
     get accessToken(): ((name: string, scopes?: string[]) => string) | undefined {
         const accessToken = this.configuration.accessToken;
-        return accessToken && (typeof accessToken === 'function' ? accessToken : () => accessToken);
+        if (!accessToken) {
+            return undefined;
+        }
+        return typeof accessToken === 'string' ? () => accessToken : accessToken;
     }
 }
 
diff --git a/samples/client/petstore/typescript-rxjs/builds/with-npm-version/runtime.ts b/samples/client/petstore/typescript-rxjs/builds/with-npm-version/runtime.ts
index 40d2e7b3947..e4c93e87e51 100644
--- a/samples/client/petstore/typescript-rxjs/builds/with-npm-version/runtime.ts
+++ b/samples/client/petstore/typescript-rxjs/builds/with-npm-version/runtime.ts
@@ -47,12 +47,18 @@ export class Configuration {
 
     get apiKey(): ((name: string) => string) | undefined {
         const apiKey = this.configuration.apiKey;
-        return apiKey && (typeof apiKey === 'function' ? apiKey : () => apiKey);
+        if (!apiKey) {
+            return undefined;
+        }
+        return typeof apiKey === 'string' ? () => apiKey : apiKey;
     }
 
     get accessToken(): ((name: string, scopes?: string[]) => string) | undefined {
         const accessToken = this.configuration.accessToken;
-        return accessToken && (typeof accessToken === 'function' ? accessToken : () => accessToken);
+        if (!accessToken) {
+            return undefined;
+        }
+        return typeof accessToken === 'string' ? () => accessToken : accessToken;
     }
 }