Fixes #16679: Avoid overwriting custom JSON fields during bulk edit

netbox/extras/models/customfields.py

@@ -490,7 +490,7 @@ class CustomField(CloningMixin, ExportTemplatesMixin, ChangeLoggedModel):
 
         # JSON
         elif self.type == CustomFieldTypeChoices.TYPE_JSON:
-            field = JSONField(required=required, initial=json.dumps(initial) if initial else '')
+            field = JSONField(required=required, initial=json.dumps(initial) if initial else None)
 
         # Object
         elif self.type == CustomFieldTypeChoices.TYPE_OBJECT: