True if this cell contains only a single empty ``<w:p>`` element.

def _is_empty(self):
        """
        True if this cell contains only a single empty ``<w:p>`` element.
        """
        block_items = list(self.iter_block_items())
        if len(block_items) > 1:
            return False
        p = block_items[0]  # cell must include at least one <w:p> element
        if len(p.r_lst) == 0:
            return True
        return False