code: @Override
  	public void invoke(IN tuple) {
  
  		tupleList.add(tuple);
  		if (updateCondition()) {
  			format.write(path, tupleList);
  			resetParameters();
  		}
  
  	}
docs: Implementation of the invoke method of the SinkFunction class. Collects
  the incoming tuples in tupleList and appends the list to the end of the
  target file if updateCondition() is true or the current tuple is the
  endTuple.