code: def _map_agent_mod(self, agent, mod_condition):
          up_id = _get_uniprot_id(agent)
          if not up_id:
              logger.debug("No uniprot ID for %s" % agent.name)
              return None
          if mod_condition.position is None or mod_condition.residue is None:
              return None
          mapped_site = \
              self.map_to_human_ref(up_id, 'uniprot',
                  mod_condition.residue,
                  mod_condition.position,
                  do_methionine_offset=self.do_methionine_offset,
                  do_orthology_mapping=self.do_orthology_mapping,
                  do_isoform_mapping=self.do_isoform_mapping)
          return mapped_site