docs: public <K extends Comparable<K>> PartitionOperator<T> partitionCustom(Partitioner<K> partitioner, KeySelector<T, K> keyExtractor) {
  		final TypeInformation<K> keyType = TypeExtractor.getKeySelectorTypes(keyExtractor, getType());
  		return new PartitionOperator<>(this, new Keys.SelectorFunctionKeys<>(keyExtractor, getType(), keyType), clean(partitioner), Utils.getCallLocationName());
  	}