docs: @Deprecated
  	public <R> SingleOutputStreamOperator<R> fold(R initialValue, FoldFunction<T, R> function) {
  		if (function instanceof RichFunction) {
  			throw new UnsupportedOperationException("FoldFunction can not be a RichFunction. " +
  				"Please use fold(FoldFunction, WindowFunction) instead.");
  		}
  
  		TypeInformation<R> resultType = TypeExtractor.getFoldReturnTypes(function, input.getType(),
  				Utils.getCallLocationName(), true);
  
  		return fold(initialValue, function, resultType);
  	}