code: public Observable<BuildTaskInner> beginUpdateAsync(String resourceGroupName, String registryName, String buildTaskName, BuildTaskUpdateParameters buildTaskUpdateParameters) {
          return beginUpdateWithServiceResponseAsync(resourceGroupName, registryName, buildTaskName, buildTaskUpdateParameters).map(new Func1<ServiceResponse<BuildTaskInner>, BuildTaskInner>() {
              @Override
              public BuildTaskInner call(ServiceResponse<BuildTaskInner> response) {
                  return response.body();
              }
          });
      }
docs: Updates a build task with the specified parameters.
  
  @param resourceGroupName The name of the resource group to which the container registry belongs.
  @param registryName The name of the container registry.
  @param buildTaskName The name of the container registry build task.
  @param buildTaskUpdateParameters The parameters for updating a build task.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the BuildTaskInner object