docs: async def get_xy_address(self, xy):
          '''Get address of the agent residing in *xy* coordinate, or ``None``
          if no such agent is in this multi-environment.
          '''
          manager_addr = self.get_xy_environment(xy)
          if manager_addr is None:
              return None
          else:
              r_agent = await self._env.connect(manager_addr)
              xy_addr = await r_agent.get_xy_address(xy)
              return xy_addr