Get address of the agent residing in *xy* coordinate, or ``None``
        if no such agent is in this multi-environment.

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