docs: @PublicEvolving
  	public SingleOutputStreamOperator<T> setMaxParallelism(int maxParallelism) {
  		Preconditions.checkArgument(maxParallelism > 0,
  				"The maximum parallelism must be greater than 0.");
  
  		Preconditions.checkArgument(canBeParallel() || maxParallelism == 1,
  				"The maximum parallelism of non parallel operator must be 1.");
  
  		transformation.setMaxParallelism(maxParallelism);
  
  		return this;
  	}