nobil migration: ignore if no realtime data exists

Author: johan12345

src/evmap_backend/data_sources/nobil/migrations/0003_remove_nobilconnector_charging_station_and_more.py

@@ -6,6 +6,10 @@
 
 
 def get_nobil_data(apps, schema_editor):
+    NobilRealtimeData = apps.get_model("nobil", "NobilRealtimeData")
+    if NobilRealtimeData.objects.count() == 0:
+        return
+
     get_data_source("nobil").pull_data()