test(devops): correct GitGroup Unit model test suite

ref: #807 closes #781

app/core/signal/centurion_model_migrate.py

@@ -112,6 +112,10 @@ def centurion_model_migrate(sender, **kwargs):
 
             try:
 
+                if history_model_name is None:
+
+                    raise LookupError('No history model to migrate')
+
                 original_history = apps.get_model(
                     app_label = app_label,
                     model_name = history_model_name
@@ -173,6 +177,11 @@ def centurion_model_migrate(sender, **kwargs):
 
         if getattr(model, '_notes_enabled', False):
 
+
+            if notes_model_name is None:
+
+                raise LookupError('No notes model to migrate')
+
             try:
 
                 original_notes = apps.get_model(