[typescript-angular] Provide return value for all code paths (#9174) (#…

…9176)

In order to avoid a compiler error when using `noImplicitReturns `, we
change the mustache template to use provide a return value for the if-
and else branch.

Fixes #9174.

modules/openapi-generator/src/main/resources/typescript-angular/configuration.mustache

@@ -70,9 +70,9 @@ export class {{configurationClassName}} {
 {{#isBasic}}
     {{#isBasicBasic}}
             this.credentials['{{name}}'] = () => {
-                if (this.username || this.password) {
-                    return btoa(this.username + ':' + this.password);
-                }
+                return (this.username || this.password)
+                    ? btoa(this.username + ':' + this.password)
+                    : undefined;
             };
     {{/isBasicBasic}}
     {{#isBasicBearer}}