code: @Override
  	public void join(IN1 value1, IN2 value2, Collector<OUT> out) throws Exception {
  		out.collect(join(value1, value2));
  	}
docs: The user-defined method for performing transformations after a join, for operations that
  produce zero elements, or more than one element.
  By default, this method delegates to the method {@link #join(Object, Object)}. If this method
  is overridden, that method will no longer be called.
  
  @param first The element from first input.
  @param second The element from second input.
  @param out A collector to emit resulting element (zero, one, or many).
  
  @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
  to fail and may trigger recovery.