[fix] Exclude location_id from radius_acc extra_tags if missing

Avoid including the `location_id` tag in `radius_acc` metrics
when the device has no associated `DeviceLocation`.

InfluxDB does not support tags with `None` values, which
causes errors when attempting to delete such metrics.

---------

Co-authored-by: Federico Capoano <f.capoano@openwisp.io>

Author: pandafy

openwisp_radius/integrations/monitoring/tasks.py

@@ -195,6 +195,12 @@ def post_save_radiusaccounting(
     else:
         registration_method = clean_registration_method(registration_method)
     device_lookup = Q(mac_address__iexact=called_station_id.replace('-', ':'))
+    extra_tags = {
+        'method': registration_method,
+        'organization_id': organization_id,
+        'calling_station_id': sha1_hash(calling_station_id),
+        'called_station_id': called_station_id,
+    }
     # Do not use organization_id for device lookup if shared accounting is enabled
     if not app_settings.SHARED_ACCOUNTING:
         device_lookup &= Q(organization_id=organization_id)
@@ -212,30 +218,21 @@ def post_save_radiusaccounting(
         )
         object_id = None
         content_type = None
-        location_id = None
         if app_settings.SHARED_ACCOUNTING:
-            organization_id = None
+            extra_tags.pop('organization_id')
     else:
         object_id = str(device.id)
         content_type = ContentType.objects.get_for_model(Device)
         if hasattr(device, 'devicelocation'):
-            location_id = str(device.devicelocation.location_id)
-        else:
-            location_id = None
+            extra_tags['location_id'] = str(device.devicelocation.location_id)
 
     metric, created = Metric._get_or_create(
         configuration='radius_acc',
         name='RADIUS Accounting',
         key='radius_acc',
         object_id=object_id,
         content_type=content_type,
-        extra_tags={
-            'organization_id': organization_id,
-            'method': registration_method,
-            'calling_station_id': sha1_hash(calling_station_id),
-            'called_station_id': called_station_id,
-            'location_id': location_id,
-        },
+        extra_tags=extra_tags,
     )
     metric.write(
         input_octets,

openwisp_radius/integrations/monitoring/tests/test_metrics.py

@@ -86,6 +86,51 @@ def test_post_save_radiusaccounting(self, *args):
         self.assertEqual(points['traces'][0][1][-1], 1)
         self.assertEqual(points['summary'], {'mobile_phone': 1})
 
+    @patch('logging.Logger.warning')
+    def test_post_save_radiusaccounting_device_without_location(self, *args):
+        user = self._create_user()
+        reg_user = self._create_registered_user(user=user)
+        device = self._create_device()
+        options = _RADACCT.copy()
+        options.update(
+            {
+                'unique_id': '117',
+                'username': user.username,
+                'called_station_id': device.mac_address.replace('-', ':').upper(),
+                'calling_station_id': '00:00:00:00:00:00',
+                'input_octets': '8000000000',
+                'output_octets': '9000000000',
+            }
+        )
+        options['stop_time'] = options['start_time']
+        self._create_radius_accounting(**options)
+        with self.subTest('location_id should not be set'):
+            self.assertEqual(
+                self.metric_model.objects.filter(
+                    configuration='radius_acc',
+                    name='RADIUS Accounting',
+                    key='radius_acc',
+                    object_id=str(device.id),
+                    content_type=ContentType.objects.get_for_model(self.device_model),
+                    extra_tags={
+                        'called_station_id': device.mac_address,
+                        'calling_station_id': sha1_hash('00:00:00:00:00:00'),
+                        'method': reg_user.method,
+                        'organization_id': str(self.default_org.id),
+                    },
+                ).count(),
+                1,
+            )
+        with self.subTest('Deleting device without location_id should not fail'):
+            self.device_model.objects.all().delete()
+            self.assertEqual(self.device_model.objects.count(), 0)
+            self.assertEqual(
+                self.metric_model.objects.filter(
+                    key='radius_acc', object_id=str(device.id)
+                ).count(),
+                0,
+            )
+
     @patch('openwisp_radius.integrations.monitoring.tasks.post_save_radiusaccounting')
     def test_post_save_radiusaccouting_open_session(self, mocked_task):
         radius_options = _RADACCT.copy()
@@ -157,7 +202,6 @@ def test_post_save_radius_accounting_shared_accounting(self, mocked_logger):
                     extra_tags={
                         'called_station_id': device.mac_address,
                         'calling_station_id': sha1_hash('00:00:00:00:00:00'),
-                        'location_id': None,
                         'method': reg_user.method,
                         'organization_id': str(self.default_org.id),
                     },
@@ -222,7 +266,6 @@ def test_post_save_radius_accounting_device_not_found(self, mocked_logger):
                 extra_tags={
                     'called_station_id': '11:22:33:44:55:66',
                     'calling_station_id': sha1_hash('00:00:00:00:00:00'),
-                    'location_id': None,
                     'method': reg_user.method,
                     'organization_id': str(self.default_org.id),
                 },