code: public Observable<ServiceResponse<DnsNameAvailabilityResultInner>> checkDnsNameAvailabilityWithServiceResponseAsync(String location, String domainNameLabel) {
          if (location == null) {
              throw new IllegalArgumentException("Parameter location is required and cannot be null.");
          }
          if (this.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.subscriptionId() is required and cannot be null.");
          }
          if (domainNameLabel == null) {
              throw new IllegalArgumentException("Parameter domainNameLabel is required and cannot be null.");
          }
          final String apiVersion = "2018-04-01";
          return service.checkDnsNameAvailability(location, this.subscriptionId(), domainNameLabel, apiVersion, this.acceptLanguage(), this.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<DnsNameAvailabilityResultInner>>>() {
                  @Override
                  public Observable<ServiceResponse<DnsNameAvailabilityResultInner>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<DnsNameAvailabilityResultInner> clientResponse = checkDnsNameAvailabilityDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Checks whether a domain name in the cloudapp.azure.com zone is available for use.
  
  @param location The location of the domain name.
  @param domainNameLabel The domain name to be verified. It must conform to the following regular expression: ^[a-z][a-z0-9-]{1,61}[a-z0-9]$.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the DnsNameAvailabilityResultInner object