docs: @PublicEvolving
  	public <R> SingleOutputStreamOperator<R> reduce(ReduceFunction<T> reduceFunction, ProcessWindowFunction<T, R, K, W> function) {
  		TypeInformation<R> resultType = getProcessWindowFunctionReturnType(function, input.getType(), null);
  
  		return reduce(reduceFunction, function, resultType);
  	}