[typescript-angular] replace Error with rxjs throwError if a parameter is missing

Description

If RxJS6 is used, the current method still has to use try-catch block.

public addPet(body: Pet, observe: any = 'body', reportProgress: boolean = false ): Observable<any> {

        if (body === null || body === undefined) {
            throw new Error('Required parameter body was null or undefined when calling addPet.');
        }
}

try {
  addPet(null).pipe(catchError(e => {
    console.log(e);
    return EMPTY;
  })).subscribe();
} catch (e) {
  console.log("Exception", e);
}

However, if throwError is used in RxJS6, api request can be simplified.

public addPet(body: SwgPetHa, observe: any = 'body', reportProgress: boolean = false ): Observable<any> {

        if (body === null || body === undefined) {
            return throwError('Required parameter body was null or undefined when calling addPet.');
        }
}
addPet(null).pipe(catchError(e => {
    console.log(e);
    return EMPTY;
  })).subscribe();

Swagger-codegen version

Swagger Codegen 2.X

Swagger declaration file content or url

Command line used for generation

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

Start by locating the TypeScript Angular templates or generator entry points that emit the required-parameter checks shown in the issue. Review how the generated addPet method handles a missing body with RxJS 6, then verify that the generated client reports the error through the observable flow without requiring an outer try-catch.