docs: def get_footerReference(self, type_):
          """Return footerReference element of *type_* or None if not present."""
          path = "./w:footerReference[@w:type='%s']" % WD_HEADER_FOOTER.to_xml(type_)
          footerReferences = self.xpath(path)
          if not footerReferences:
              return None
          return footerReferences[0]