message: fix: closure compiler warning
  PR Close
diff: @@ -310,7 +310,7 @@ export class PlatformRef_ extends PlatformRef {
  private _bootstrapModuleWithZone<M>(
  moduleType: Type<M>, compilerOptions: CompilerOptions|CompilerOptions[] = [],
  - ngZone: NgZone): Promise<NgModuleRef<M>> {
  + ngZone: NgZone = null): Promise<NgModuleRef<M>> {
  const compilerFactory: CompilerFactory = this.injector.get(CompilerFactory);
  const compiler = compilerFactory.createCompiler(
  Array.isArray(compilerOptions) ? compilerOptions : [compilerOptions]);
  