fix: ignore string literals 'null' and 'undefined' from frontend form data for optional fields

routes/translate_routes.py

@@ -526,6 +526,13 @@ async def translate_document_v1(
             tier = _tier_for_quota(current_user.plan)
             user_id = current_user.id
 
+        # Clean up form data (frontend might send "null" or "undefined" as strings)
+        if glossary_id in ("null", "undefined", ""): glossary_id = None
+        if custom_prompt in ("null", "undefined", ""): custom_prompt = None
+        if prompt_id in ("null", "undefined", ""): prompt_id = None
+        if file_url in ("null", "undefined", ""): file_url = None
+
+
         if file_url:
             if tier == "free":
                 raise TranslateEndpointError(