docs: public <R> SingleOutputStreamOperator<R> flatMap(FlatMapFunction<T, R> flatMapper) {
  
  		TypeInformation<R> outType = TypeExtractor.getFlatMapReturnTypes(clean(flatMapper),
  				getType(), Utils.getCallLocationName(), true);
  
  		return transform("Flat Map", outType, new StreamFlatMap<>(clean(flatMapper)));
  
  	}