Return the text in the element matching *property_name*, or an empty
        string if the element is not present or contains no text.

def _text_of_element(self, property_name):
        """
        Return the text in the element matching *property_name*, or an empty
        string if the element is not present or contains no text.
        """
        element = getattr(self, property_name)
        if element is None:
            return ''
        if element.text is None:
            return ''
        return element.text