docs: @Deprecated
  	public <R> SingleOutputStreamOperator<R> fold(R initialValue, FoldFunction<T, R> folder) {
  
  		TypeInformation<R> outType = TypeExtractor.getFoldReturnTypes(
  				clean(folder), getType(), Utils.getCallLocationName(), true);
  
  		return transform("Keyed Fold", outType, new StreamGroupedFold<>(clean(folder), initialValue));
  	}