diff --git a/modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache b/modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache
index 02632f0c64c7..40aaec67f477 100644
--- a/modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache
@@ -64,7 +64,11 @@ export class {{configurationClassName}} {
 {{#isApiKey}}
             this.credentials['{{name}}'] = () => {
                 {{! Fallback behaviour may be removed for 5.0 release. See #5062 }}
-                return this.apiKeys['{{name}}'] || this.apiKeys['{{keyParamName}}'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['{{name}}'] || this.apiKeys['{{keyParamName}}'];
+                }
             };
 {{/isApiKey}}
 {{#isBasic}}
diff --git a/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v10-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v11-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/configuration.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/configuration.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/configuration.ts
index 1bd306a523eb..900c26d8ebfe 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/configuration.ts
@@ -61,7 +61,11 @@ export class PetStoreConfiguration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v9-provided-in-any/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v9-provided-in-any/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v9-provided-in-any/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v9-provided-in-any/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/default/configuration.ts b/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/default/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/default/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/default/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }
 
diff --git a/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/with-npm/configuration.ts b/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/with-npm/configuration.ts
index 38126642420d..6fc0f80d973f 100644
--- a/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/with-npm/configuration.ts
+++ b/samples/client/petstore/typescript-angular-v9-provided-in-root/builds/with-npm/configuration.ts
@@ -61,7 +61,11 @@ export class Configuration {
         // init default api_key credential
         if (!this.credentials['api_key']) {
             this.credentials['api_key'] = () => {
-                return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                if (this.apiKeys === null || this.apiKeys === undefined) {
+                    return undefined;
+                } else {
+                    return this.apiKeys['api_key'] || this.apiKeys['api_key'];
+                }
             };
         }