code: public ServiceFuture<CloudTaskListSubtasksResult> listSubtasksAsync(String jobId, String taskId, TaskListSubtasksOptions taskListSubtasksOptions, final ServiceCallback<CloudTaskListSubtasksResult> serviceCallback) {
          return ServiceFuture.fromHeaderResponse(listSubtasksWithServiceResponseAsync(jobId, taskId, taskListSubtasksOptions), serviceCallback);
      }
docs: Lists all of the subtasks that are associated with the specified multi-instance task.
  If the task is not a multi-instance task then this returns an empty collection.
  
  @param jobId The ID of the job.
  @param taskId The ID of the task.
  @param taskListSubtasksOptions Additional parameters for the operation
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object