diff --git a/modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache b/modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache
index 38ffa081b85a..35c15e870c65 100644
--- a/modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache
+++ b/modules/openapi-generator/src/main/resources/typescript-angular/api.service.mustache
@@ -278,18 +278,19 @@ export class {{classname}} {
 {{#authMethods}}
         // authentication ({{name}}) required
 {{#isApiKey}}
+        if (this.configuration.apiKeys) {
+            {{! Fallback behaviour may be removed for 5.0 release. See #5062 }}
+            const key: string | undefined = this.configuration.apiKeys["{{name}}"] || this.configuration.apiKeys["{{keyParamName}}"];
+            if (key) {
 {{#isKeyInHeader}}
-        if (this.configuration.apiKeys && this.configuration.apiKeys["{{keyParamName}}"]) {
-            {{#useHttpClient}}headers = {{/useHttpClient}}headers.set('{{keyParamName}}', this.configuration.apiKeys["{{keyParamName}}"]);
-        }
-
+                {{#useHttpClient}}headers = {{/useHttpClient}}headers.set('{{keyParamName}}', key);
 {{/isKeyInHeader}}
 {{#isKeyInQuery}}
-        if (this.configuration.apiKeys && this.configuration.apiKeys["{{keyParamName}}"]) {
-            {{#useHttpClient}}queryParameters = {{/useHttpClient}}queryParameters.set('{{keyParamName}}', this.configuration.apiKeys["{{keyParamName}}"]);
+                {{#useHttpClient}}queryParameters = {{/useHttpClient}}queryParameters.set('{{keyParamName}}', key);
+{{/isKeyInQuery}}
+            }
         }
 
-{{/isKeyInQuery}}
 {{/isApiKey}}
 {{#isBasic}}
     {{#isBasicBasic}}
diff --git a/samples/client/petstore/typescript-angular-v2/default/api/pet.service.ts b/samples/client/petstore/typescript-angular-v2/default/api/pet.service.ts
index a2a05d7464ed..8a80a3026a05 100644
--- a/samples/client/petstore/typescript-angular-v2/default/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/default/api/pet.service.ts
@@ -468,8 +468,11 @@ export class PetService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v2/default/api/store.service.ts b/samples/client/petstore/typescript-angular-v2/default/api/store.service.ts
index 3cff4ba2c0ea..0d64a469bdff 100644
--- a/samples/client/petstore/typescript-angular-v2/default/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/default/api/store.service.ts
@@ -199,8 +199,11 @@ export class StoreService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v2/npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v2/npm/api/pet.service.ts
index a2a05d7464ed..8a80a3026a05 100644
--- a/samples/client/petstore/typescript-angular-v2/npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/npm/api/pet.service.ts
@@ -468,8 +468,11 @@ export class PetService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v2/npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v2/npm/api/store.service.ts
index 3cff4ba2c0ea..0d64a469bdff 100644
--- a/samples/client/petstore/typescript-angular-v2/npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/npm/api/store.service.ts
@@ -199,8 +199,11 @@ export class StoreService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v2/with-interfaces/api/pet.service.ts b/samples/client/petstore/typescript-angular-v2/with-interfaces/api/pet.service.ts
index b3230d244e2a..2d153ab2ba5f 100644
--- a/samples/client/petstore/typescript-angular-v2/with-interfaces/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/with-interfaces/api/pet.service.ts
@@ -471,8 +471,11 @@ export class PetService implements PetServiceInterface {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v2/with-interfaces/api/store.service.ts b/samples/client/petstore/typescript-angular-v2/with-interfaces/api/store.service.ts
index f945e50874c8..5aa28658557e 100644
--- a/samples/client/petstore/typescript-angular-v2/with-interfaces/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v2/with-interfaces/api/store.service.ts
@@ -202,8 +202,11 @@ export class StoreService implements StoreServiceInterface {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v4.3/npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v4.3/npm/api/pet.service.ts
index b5bf94fba2c6..b19fbc6c6bfe 100644
--- a/samples/client/petstore/typescript-angular-v4.3/npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v4.3/npm/api/pet.service.ts
@@ -358,8 +358,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v4.3/npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v4.3/npm/api/store.service.ts
index 6e521f729e49..2a335a30d08b 100644
--- a/samples/client/petstore/typescript-angular-v4.3/npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v4.3/npm/api/store.service.ts
@@ -142,8 +142,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v4/npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v4/npm/api/pet.service.ts
index a2a05d7464ed..8a80a3026a05 100644
--- a/samples/client/petstore/typescript-angular-v4/npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v4/npm/api/pet.service.ts
@@ -468,8 +468,11 @@ export class PetService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v4/npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v4/npm/api/store.service.ts
index 3cff4ba2c0ea..0d64a469bdff 100644
--- a/samples/client/petstore/typescript-angular-v4/npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v4/npm/api/store.service.ts
@@ -199,8 +199,11 @@ export class StoreService {
         let headers = new Headers(this.defaultHeaders.toJSON()); // https://github.com/angular/angular/issues/6845
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/pet.service.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/pet.service.ts
index 35d6f883accc..8f9c55158bb3 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/pet.service.ts
@@ -358,8 +358,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/store.service.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/store.service.ts
index 22db3e3008b2..d27113a8b528 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/default/api/store.service.ts
@@ -142,8 +142,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/pet.service.ts
index 35d6f883accc..8f9c55158bb3 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/pet.service.ts
@@ -358,8 +358,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/store.service.ts
index 22db3e3008b2..d27113a8b528 100644
--- a/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-not-provided-in-root/builds/with-npm/api/store.service.ts
@@ -142,8 +142,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/pet.service.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/store.service.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/default/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v6-provided-in-root/builds/with-npm/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/pet.service.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/pet.service.ts
index 35d6f883accc..8f9c55158bb3 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/pet.service.ts
@@ -358,8 +358,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/store.service.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/store.service.ts
index 22db3e3008b2..d27113a8b528 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/default/api/store.service.ts
@@ -142,8 +142,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/pet.service.ts
index 35d6f883accc..8f9c55158bb3 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/pet.service.ts
@@ -358,8 +358,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/store.service.ts
index 22db3e3008b2..d27113a8b528 100644
--- a/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-not-provided-in-root/builds/with-npm/api/store.service.ts
@@ -142,8 +142,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/pet.service.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/store.service.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/default/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v7-provided-in-root/builds/with-npm/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/pet.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/pet.service.ts
index 0e2f4d61ae20..7457b9bf3c43 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/pet.service.ts
@@ -402,8 +402,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/store.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/store.service.ts
index ec3164d42299..b0d5dd8b4e50 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/single-request-parameter/api/store.service.ts
@@ -157,8 +157,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/pet.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/store.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-npm/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/pet.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/pet.service.ts
index 91bbce5b7476..1d81cf38c3d6 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/pet.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/pet.service.ts
@@ -360,8 +360,11 @@ export class PetService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;
diff --git a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/store.service.ts b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/store.service.ts
index d169e06083a5..c6e1ea7214e6 100644
--- a/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/store.service.ts
+++ b/samples/client/petstore/typescript-angular-v8-provided-in-root/builds/with-prefixed-module-name/api/store.service.ts
@@ -144,8 +144,11 @@ export class StoreService {
         let headers = this.defaultHeaders;
 
         // authentication (api_key) required
-        if (this.configuration.apiKeys && this.configuration.apiKeys["api_key"]) {
-            headers = headers.set('api_key', this.configuration.apiKeys["api_key"]);
+        if (this.configuration.apiKeys) {
+            const key: string | undefined = this.configuration.apiKeys["api_key"] || this.configuration.apiKeys["api_key"];
+            if (key) {
+                headers = headers.set('api_key', key);
+            }
         }
 
         let httpHeaderAcceptSelected: string | undefined = options && options.httpHeaderAccept;