Call super().clean() after validating scope_type/scope

netbox/dcim/models/mixins.py

@@ -94,6 +94,7 @@ def clean(self):
                     "Please select a {scope_type}."
                 ).format(scope_type=scope_type._meta.model_name)
             })
+        super().clean()
 
     def save(self, *args, **kwargs):
         # Cache objects associated with the terminating object (for filtering)