code: private void checkDataSink(GenericDataSinkBase<?> dataSinkContract) {
  		Operator<?> input = dataSinkContract.getInput();
  		// check if input exists
  		if (input == null) {
  			throw new MissingChildException();
  		}
  	}
docs: Checks if DataSinkContract is correctly connected. In case that the
  contract is incorrectly connected a RuntimeException is thrown.
  
  @param dataSinkContract
  DataSinkContract that is checked.