[Bug] fix: use length to check for default return media type (#15833)

* fix: use length to check for default return media type

as `mediaTypes` is an array of strings and an required argument
it will never be undefined when we can rely on the typesystem.
However, it can be zero length(`[]`) and in this case we would
throw.

* Closes #15011

* chore: update examples

modules/openapi-generator/src/main/resources/typescript/model/ObjectSerializer.mustache

@@ -196,7 +196,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/client/others/typescript/builds/with-unique-items/models/ObjectSerializer.ts

@@ -168,7 +168,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/browser/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/composed-schemas/models/ObjectSerializer.ts

@@ -190,7 +190,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/default/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/deno/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/inversify/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/jquery/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }
 

samples/openapi3/client/petstore/typescript/builds/object_params/models/ObjectSerializer.ts

@@ -185,7 +185,7 @@ export class ObjectSerializer {
      */
     public static getPreferredMediaType(mediaTypes: Array<string>): string {
         /** According to OAS 3 we should default to json */
-        if (!mediaTypes) {
+        if (mediaTypes.length === 0) {
             return "application/json";
         }