code: public Observable<ServiceResponse<TagDetailsInner>> createOrUpdateWithServiceResponseAsync(String tagName) {
          if (tagName == null) {
              throw new IllegalArgumentException("Parameter tagName 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.createOrUpdate(tagName, this.client.subscriptionId(), this.client.apiVersion(), this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<TagDetailsInner>>>() {
                  @Override
                  public Observable<ServiceResponse<TagDetailsInner>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<TagDetailsInner> clientResponse = createOrUpdateDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Creates a tag in the subscription.
  The tag name can have a maximum of 512 characters and is case insensitive. Tag names created by Azure have prefixes of microsoft, azure, or windows. You cannot create tags with one of these prefixes.
  
  @param tagName The name of the tag to create.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the TagDetailsInner object