Returns True if all child date elements present are empty
        and other nodes are not set.  Returns False if any child date
        elements are not empty or other nodes are set.

def is_empty(self):
        """Returns True if all child date elements present are empty
        and other nodes are not set.  Returns False if any child date
        elements are not empty or other nodes are set."""
        return all(date.is_empty() for date in [self.created, self.issued]) \
               and not self.publisher