fixed: variable reference error (#9722)

Co-authored-by: hobo.l <hobo.l@binance.com>

api/core/app/apps/message_based_app_generator.py

@@ -27,6 +27,7 @@ from core.app.task_pipeline.easy_ui_based_generate_task_pipeline import EasyUIBa
 from core.prompt.utils.prompt_template_parser import PromptTemplateParser
 from extensions.ext_database import db
 from models import Account
+from models.enums import CreatedByRole
 from models.model import App, AppMode, AppModelConfig, Conversation, EndUser, Message, MessageFile
 from services.errors.app_model_config import AppModelConfigBrokenError
 from services.errors.conversation import ConversationCompletedError, ConversationNotExistsError
@@ -240,7 +241,7 @@ class MessageBasedAppGenerator(BaseAppGenerator):
                 belongs_to="user",
                 url=file.remote_url,
                 upload_file_id=file.related_id,
-                created_by_role=("account" if account_id else "end_user"),
+                created_by_role=(CreatedByRole.ACCOUNT if account_id else CreatedByRole.END_USER),
                 created_by=account_id or end_user_id or "",
             )
             db.session.add(message_file)