code: def update_protocol_agent(self, protocol_agent):
          
          if not protocol_agent:
              for pa in ('paValues', 'protocol_agent_ref'):
                  self.data.pop(pa, None)
          else:
              self.data.update(protocol_agent_ref=element_resolver(protocol_agent))
docs: Update this service to use the specified protocol agent.
          After adding the protocol agent to the service you must call
          `update` on the element to commit.
          
          :param str,ProtocolAgent protocol_agent: protocol agent element or href
          :return: None