Please help me to solve this issue..:(

{"message":"Odoo Server Error","code":200,"data":{"debug":"Traceback (most recent call last):\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 642, in _handle_exception\n return super(JsonRequest, self)._handle_exception(exception)\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 684, in dispatch\n result = self._call_function(**self.params)\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 334, in _call_function\n return checked_call(self.db, *args, **kwargs)\n File \"\/opt\/odoo\/odoo10c\/odoo\/service\/model.py\", line 119, in wrapper\n return f(dbname, *args, **kwargs)\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 327, in checked_call\n result = self.endpoint(*a, **kw)\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 942, in __call__\n return self.method(*args, **kw)\n File \"\/opt\/odoo\/odoo10c\/odoo\/http.py\", line 507, in response_wrap\n response = f(*args, **kw)\n File \"\/opt\/odoo\/addons-micollege\/smartcollege_api\/controllers\/main.py\", line 496, in mobile_get_message_list_micollege\n return self._poll(request.db, [], request.params.get('last_notification', 0), {'group_by_author': True})\n File \"\/opt\/odoo\/addons-micollege\/smartcollege_api\/controllers\/bus.py\", line 18, in _poll\n res = super(TrackingBusController, self)._poll(dbname, channels, last, options)\n File \"\/opt\/odoo\/odoo10c\/addons\/mail\/controllers\/bus.py\", line 32, in _poll\n return super(MailChatController, self)._poll(dbname, channels, last, options)\n File \"\/opt\/odoo\/odoo10c\/addons\/calendar\/controllers\/bus.py\", line 14, in _poll\n return super(CalendarBusController, self)._poll(dbname, channels, last, options)\n File \"\/opt\/odoo\/odoo10c\/addons\/bus\/controllers\/main.py\", line 30, in _poll\n return dispatch.poll(dbname, channels, last, options)\nAttributeError: 'NoneType' object has no attribute 'poll'\n","exception_type":"internal_error","message":"'NoneType' object has no attribute 'poll'","name":"exceptions.AttributeError","arguments":["'NoneType' object has no attribute 'poll'"]}}