test: add test and simplify condition

Author: simllll

packages/cli/src/metadataGeneration/parameterGenerator.ts

@@ -440,7 +440,7 @@ export class ParameterGenerator {
 
     if (parameterType.dataType === 'union') {
       // skip undefined inside unions
-      return !parameterType.types.map(t => t.dataType === 'undefined' ? true : this.supportPathDataType(t)).some(t => t === false); 
+      return !parameterType.types.map(t => t.dataType === 'undefined' || this.supportPathDataType(t)).some(t => t === false);
     }
 
     return false;

tests/fixtures/controllers/getController.ts

@@ -327,6 +327,11 @@ export class GetTestController extends Controller {
   public async getIndexedValueGeneric(): Promise<IndexedValueGeneric<IndexedValueTypeReference>> {
     return 'FOO';
   }
+
+  @Get('UnionTypeWithDefault')
+  public async getUnionTypeWithDefault(@Query() unionType: 'a' | 'b' | undefined = 'a'): Promise<void> {
+    return;
+  }
 }
 
 export interface ErrorResponse {