code: private TaskDescriptor createTaskDescriptorForStreamCombineOperations(DStreamOperation streamOperation){
  
  		TaskDescriptor taskDescriptor = this.createTaskDescriptor(streamOperation.getLastOperationName());
  		for (DStreamExecutionGraph dependentOps : streamOperation.getCombinableExecutionGraphs()) {
  			TaskDescriptorChainBuilder builder = new TaskDescriptorChainBuilder(executionName, dependentOps, executionConfig);
  			List<TaskDescriptor> dependentDescriptors = builder.build();
  			taskDescriptor.addDependentTasksChain(dependentDescriptors);
  		}
  		return taskDescriptor;
  	}
docs: Creates {@link TaskDescriptor} for stream combine operations (i.e., join, union, unionAll)