fix no modual error (#1892)

### What problem does this PR solve?

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/file_service.py

@@ -14,7 +14,7 @@
 #  limitations under the License.
 #
 import re
-
+import os
 from flask_login import current_user
 from peewee import fn