code: public Observable<ServiceResponse<Boolean>> checkExistenceWithServiceResponseAsync(String resourceGroupName) {
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (this.client.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.client.subscriptionId() is required and cannot be null.");
          }
          if (this.client.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.client.apiVersion() is required and cannot be null.");
          }
          return service.checkExistence(resourceGroupName, this.client.subscriptionId(), this.client.apiVersion(), this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<Void>, Observable<ServiceResponse<Boolean>>>() {
                  @Override
                  public Observable<ServiceResponse<Boolean>> call(Response<Void> response) {
                      try {
                          ServiceResponse<Boolean> clientResponse = checkExistenceDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Checks whether a resource group exists.
  
  @param resourceGroupName The name of the resource group to check. The name is case insensitive.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the Boolean object