diff --git a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
index f3732e6b0cb..4cf22e11aa4 100644
--- a/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
@@ -24,7 +24,7 @@ import {
 {{#allParams.0}}
 export interface {{#prefixParameterInterfaces}}{{classname}}{{/prefixParameterInterfaces}}{{operationIdCamelCase}}Request {
 {{#allParams}}
-    {{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{#hasReadOnly}}Omit<{{{dataType}}}, {{#readOnlyVars}}'{{baseName}}'{{^-last}}|{{/-last}}{{/readOnlyVars}}>{{/hasReadOnly}}{{^hasReadOnly}}{{{dataType}}}{{/hasReadOnly}}{{#isNullable}}{{#required}} | null{{/required}}{{/isNullable}}{{/isEnum}};
+    {{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{#hasReadOnly}}Omit<{{{dataType}}}, {{#readOnlyVars}}'{{baseName}}'{{^-last}}|{{/-last}}{{/readOnlyVars}}>{{/hasReadOnly}}{{^hasReadOnly}}{{{dataType}}}{{/hasReadOnly}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}};
 {{/allParams}}
 }
 
@@ -70,7 +70,7 @@ export interface {{classname}}Interface {
      {{/isDeprecated}}
      */
     {{^useSingleRequestParameter}}
-    {{nickname}}({{#allParams}}{{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{#isNullable}}{{#required}} | null{{/required}}{{/isNullable}}{{/isEnum}}, {{/allParams}}initOverrides?: RequestInit | runtime.InitOverrideFunction): Promise<{{{returnType}}}{{^returnType}}void{{/returnType}}>;
+    {{nickname}}({{#allParams}}{{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}}, {{/allParams}}initOverrides?: RequestInit | runtime.InitOverrideFunction): Promise<{{{returnType}}}{{^returnType}}void{{/returnType}}>;
     {{/useSingleRequestParameter}}
     {{#useSingleRequestParameter}}
     {{nickname}}({{#allParams.0}}requestParameters: {{#prefixParameterInterfaces}}{{classname}}{{/prefixParameterInterfaces}}{{operationIdCamelCase}}Request, {{/allParams.0}}initOverrides?: RequestInit | runtime.InitOverrideFunction): Promise<{{{returnType}}}{{^returnType}}void{{/returnType}}>;
@@ -354,7 +354,7 @@ export class {{classname}} extends runtime.BaseAPI {
      {{/isDeprecated}}
      */
     {{^useSingleRequestParameter}}
-    async {{nickname}}({{#allParams}}{{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{#isNullable}}{{#required}} | null{{/required}}{{/isNullable}}{{/isEnum}}, {{/allParams}}initOverrides?: RequestInit | runtime.InitOverrideFunction): Promise<{{{returnType}}}{{#returnType}}{{#isResponseOptional}} | null | undefined {{/isResponseOptional}}{{/returnType}}{{^returnType}}void{{/returnType}}> {
+    async {{nickname}}({{#allParams}}{{paramName}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}}, {{/allParams}}initOverrides?: RequestInit | runtime.InitOverrideFunction): Promise<{{{returnType}}}{{#returnType}}{{#isResponseOptional}} | null | undefined {{/isResponseOptional}}{{/returnType}}{{^returnType}}void{{/returnType}}> {
         {{#returnType}}
         const response = await this.{{nickname}}Raw({{#allParams.0}}{ {{#allParams}}{{paramName}}: {{paramName}}{{^-last}}, {{/-last}}{{/allParams}} }, {{/allParams.0}}initOverrides);
         {{#isResponseOptional}}
diff --git a/modules/openapi-generator/src/main/resources/typescript-fetch/modelGenericInterfaces.mustache b/modules/openapi-generator/src/main/resources/typescript-fetch/modelGenericInterfaces.mustache
index 4b8bfa06a1b..68e5747598a 100644
--- a/modules/openapi-generator/src/main/resources/typescript-fetch/modelGenericInterfaces.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-fetch/modelGenericInterfaces.mustache
@@ -16,7 +16,7 @@ export interface {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{
      * @deprecated
     {{/deprecated}}
      */
-    {{#isReadOnly}}readonly {{/isReadOnly}}{{name}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{#isNullable}}{{#required}} | null{{/required}}{{/isNullable}}{{/isEnum}}{{^isEnum}}{{{datatype}}}{{#isNullable}}{{#required}} | null{{/required}}{{/isNullable}}{{/isEnum}};
+    {{#isReadOnly}}readonly {{/isReadOnly}}{{name}}{{^required}}?{{/required}}: {{#isEnum}}{{{datatypeWithEnum}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}}{{^isEnum}}{{{datatype}}}{{#isNullable}} | null{{/isNullable}}{{/isEnum}};
 {{/vars}}
 }{{#hasEnums}}
 
diff --git a/samples/client/petstore/typescript-fetch/builds/allOf-nullable/models/Club.ts b/samples/client/petstore/typescript-fetch/builds/allOf-nullable/models/Club.ts
index 6f935b2048d..fade52e7172 100644
--- a/samples/client/petstore/typescript-fetch/builds/allOf-nullable/models/Club.ts
+++ b/samples/client/petstore/typescript-fetch/builds/allOf-nullable/models/Club.ts
@@ -31,7 +31,7 @@ export interface Club {
      * @type {Owner}
      * @memberof Club
      */
-    owner?: Owner;
+    owner?: Owner | null;
 }
 
 /**
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/EnumTest.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/EnumTest.ts
index b4ef265fd2d..0ed65225ddc 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/EnumTest.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/EnumTest.ts
@@ -73,7 +73,7 @@ export interface EnumTest {
      * @type {OuterEnum}
      * @memberof EnumTest
      */
-    outerEnum?: OuterEnum;
+    outerEnum?: OuterEnum | null;
     /**
      * 
      * @type {OuterEnumInteger}
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/HealthCheckResult.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/HealthCheckResult.ts
index 450b2c25043..c921f52f4c9 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/HealthCheckResult.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/HealthCheckResult.ts
@@ -24,7 +24,7 @@ export interface HealthCheckResult {
      * @type {string}
      * @memberof HealthCheckResult
      */
-    nullableMessage?: string;
+    nullableMessage?: string | null;
 }
 
 /**
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/NullableClass.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/NullableClass.ts
index 2fbcea7c6ea..3f13364442d 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/NullableClass.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/NullableClass.ts
@@ -25,49 +25,49 @@ export interface NullableClass {
      * @type {number}
      * @memberof NullableClass
      */
-    integerProp?: number;
+    integerProp?: number | null;
     /**
      * 
      * @type {number}
      * @memberof NullableClass
      */
-    numberProp?: number;
+    numberProp?: number | null;
     /**
      * 
      * @type {boolean}
      * @memberof NullableClass
      */
-    booleanProp?: boolean;
+    booleanProp?: boolean | null;
     /**
      * 
      * @type {string}
      * @memberof NullableClass
      */
-    stringProp?: string;
+    stringProp?: string | null;
     /**
      * 
      * @type {Date}
      * @memberof NullableClass
      */
-    dateProp?: Date;
+    dateProp?: Date | null;
     /**
      * 
      * @type {Date}
      * @memberof NullableClass
      */
-    datetimeProp?: Date;
+    datetimeProp?: Date | null;
     /**
      * 
      * @type {Array<object>}
      * @memberof NullableClass
      */
-    arrayNullableProp?: Array<object>;
+    arrayNullableProp?: Array<object> | null;
     /**
      * 
      * @type {Array<object>}
      * @memberof NullableClass
      */
-    arrayAndItemsNullableProp?: Array<object>;
+    arrayAndItemsNullableProp?: Array<object> | null;
     /**
      * 
      * @type {Array<object>}
@@ -79,13 +79,13 @@ export interface NullableClass {
      * @type {{ [key: string]: object; }}
      * @memberof NullableClass
      */
-    objectNullableProp?: { [key: string]: object; };
+    objectNullableProp?: { [key: string]: object; } | null;
     /**
      * 
      * @type {{ [key: string]: object | null; }}
      * @memberof NullableClass
      */
-    objectAndItemsNullableProp?: { [key: string]: object | null; };
+    objectAndItemsNullableProp?: { [key: string]: object | null; } | null;
     /**
      * 
      * @type {{ [key: string]: object | null; }}
diff --git a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/ParentWithNullable.ts b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/ParentWithNullable.ts
index 81195930614..934f2f9d633 100644
--- a/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/ParentWithNullable.ts
+++ b/samples/client/petstore/typescript-fetch/builds/default-v3.0/models/ParentWithNullable.ts
@@ -31,7 +31,7 @@ export interface ParentWithNullable {
      * @type {string}
      * @memberof ParentWithNullable
      */
-    nullableProperty?: string;
+    nullableProperty?: string | null;
 }
 
 
diff --git a/samples/client/petstore/typescript-fetch/builds/enum/apis/DefaultApi.ts b/samples/client/petstore/typescript-fetch/builds/enum/apis/DefaultApi.ts
index 2ce4f1d2cf4..88a965dfc12 100644
--- a/samples/client/petstore/typescript-fetch/builds/enum/apis/DefaultApi.ts
+++ b/samples/client/petstore/typescript-fetch/builds/enum/apis/DefaultApi.ts
@@ -40,9 +40,9 @@ export interface FakeEnumRequestGetInlineRequest {
 
 export interface FakeEnumRequestGetRefRequest {
     stringEnum?: StringEnum;
-    nullableStringEnum?: StringEnum;
+    nullableStringEnum?: StringEnum | null;
     numberEnum?: NumberEnum;
-    nullableNumberEnum?: NumberEnum;
+    nullableNumberEnum?: NumberEnum | null;
 }
 
 export interface FakeEnumRequestPostInlineRequest {
diff --git a/samples/client/petstore/typescript-fetch/builds/enum/models/EnumPatternObject.ts b/samples/client/petstore/typescript-fetch/builds/enum/models/EnumPatternObject.ts
index 8f61f66faaa..fc2c493f04c 100644
--- a/samples/client/petstore/typescript-fetch/builds/enum/models/EnumPatternObject.ts
+++ b/samples/client/petstore/typescript-fetch/builds/enum/models/EnumPatternObject.ts
@@ -43,7 +43,7 @@ export interface EnumPatternObject {
      * @type {StringEnum}
      * @memberof EnumPatternObject
      */
-    nullableStringEnum?: StringEnum;
+    nullableStringEnum?: StringEnum | null;
     /**
      * 
      * @type {NumberEnum}
@@ -55,7 +55,7 @@ export interface EnumPatternObject {
      * @type {NumberEnum}
      * @memberof EnumPatternObject
      */
-    nullableNumberEnum?: NumberEnum;
+    nullableNumberEnum?: NumberEnum | null;
 }
 
 /**
diff --git a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/EnumTest.ts b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/EnumTest.ts
index b4ef265fd2d..0ed65225ddc 100644
--- a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/EnumTest.ts
+++ b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/EnumTest.ts
@@ -73,7 +73,7 @@ export interface EnumTest {
      * @type {OuterEnum}
      * @memberof EnumTest
      */
-    outerEnum?: OuterEnum;
+    outerEnum?: OuterEnum | null;
     /**
      * 
      * @type {OuterEnumInteger}
diff --git a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/HealthCheckResult.ts b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/HealthCheckResult.ts
index 450b2c25043..c921f52f4c9 100644
--- a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/HealthCheckResult.ts
+++ b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/HealthCheckResult.ts
@@ -24,7 +24,7 @@ export interface HealthCheckResult {
      * @type {string}
      * @memberof HealthCheckResult
      */
-    nullableMessage?: string;
+    nullableMessage?: string | null;
 }
 
 /**
diff --git a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/NullableClass.ts b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/NullableClass.ts
index 2fbcea7c6ea..3f13364442d 100644
--- a/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/NullableClass.ts
+++ b/samples/client/petstore/typescript-fetch/builds/snakecase-discriminator/models/NullableClass.ts
@@ -25,49 +25,49 @@ export interface NullableClass {
      * @type {number}
      * @memberof NullableClass
      */
-    integerProp?: number;
+    integerProp?: number | null;
     /**
      * 
      * @type {number}
      * @memberof NullableClass
      */
-    numberProp?: number;
+    numberProp?: number | null;
     /**
      * 
      * @type {boolean}
      * @memberof NullableClass
      */
-    booleanProp?: boolean;
+    booleanProp?: boolean | null;
     /**
      * 
      * @type {string}
      * @memberof NullableClass
      */
-    stringProp?: string;
+    stringProp?: string | null;
     /**
      * 
      * @type {Date}
      * @memberof NullableClass
      */
-    dateProp?: Date;
+    dateProp?: Date | null;
     /**
      * 
      * @type {Date}
      * @memberof NullableClass
      */
-    datetimeProp?: Date;
+    datetimeProp?: Date | null;
     /**
      * 
      * @type {Array<object>}
      * @memberof NullableClass
      */
-    arrayNullableProp?: Array<object>;
+    arrayNullableProp?: Array<object> | null;
     /**
      * 
      * @type {Array<object>}
      * @memberof NullableClass
      */
-    arrayAndItemsNullableProp?: Array<object>;
+    arrayAndItemsNullableProp?: Array<object> | null;
     /**
      * 
      * @type {Array<object>}
@@ -79,13 +79,13 @@ export interface NullableClass {
      * @type {{ [key: string]: object; }}
      * @memberof NullableClass
      */
-    objectNullableProp?: { [key: string]: object; };
+    objectNullableProp?: { [key: string]: object; } | null;
     /**
      * 
      * @type {{ [key: string]: object | null; }}
      * @memberof NullableClass
      */
-    objectAndItemsNullableProp?: { [key: string]: object | null; };
+    objectAndItemsNullableProp?: { [key: string]: object | null; } | null;
     /**
      * 
      * @type {{ [key: string]: object | null; }}
diff --git a/samples/client/petstore/typescript-fetch/builds/with-string-enums/apis/DefaultApi.ts b/samples/client/petstore/typescript-fetch/builds/with-string-enums/apis/DefaultApi.ts
index e9c2a1b83cf..8eb16afcbf4 100644
--- a/samples/client/petstore/typescript-fetch/builds/with-string-enums/apis/DefaultApi.ts
+++ b/samples/client/petstore/typescript-fetch/builds/with-string-enums/apis/DefaultApi.ts
@@ -40,9 +40,9 @@ export interface FakeEnumRequestGetInlineRequest {
 
 export interface FakeEnumRequestGetRefRequest {
     stringEnum?: StringEnum;
-    nullableStringEnum?: StringEnum;
+    nullableStringEnum?: StringEnum | null;
     numberEnum?: NumberEnum;
-    nullableNumberEnum?: NumberEnum;
+    nullableNumberEnum?: NumberEnum | null;
 }
 
 export interface FakeEnumRequestPostInlineRequest {
diff --git a/samples/client/petstore/typescript-fetch/builds/with-string-enums/models/EnumPatternObject.ts b/samples/client/petstore/typescript-fetch/builds/with-string-enums/models/EnumPatternObject.ts
index 8f61f66faaa..fc2c493f04c 100644
--- a/samples/client/petstore/typescript-fetch/builds/with-string-enums/models/EnumPatternObject.ts
+++ b/samples/client/petstore/typescript-fetch/builds/with-string-enums/models/EnumPatternObject.ts
@@ -43,7 +43,7 @@ export interface EnumPatternObject {
      * @type {StringEnum}
      * @memberof EnumPatternObject
      */
-    nullableStringEnum?: StringEnum;
+    nullableStringEnum?: StringEnum | null;
     /**
      * 
      * @type {NumberEnum}
@@ -55,7 +55,7 @@ export interface EnumPatternObject {
      * @type {NumberEnum}
      * @memberof EnumPatternObject
      */
-    nullableNumberEnum?: NumberEnum;
+    nullableNumberEnum?: NumberEnum | null;
 }
 
 /**