Drobox Backup Upload Failed!

any idea about this error?

Backup Upload Failed!

Oops, your automated backup to Dropbox failed.

Error message: Traceback (most recent call last): File “/home/frappe/frappe-bench/apps/frappe/frappe/integrations/doctype/dropbox_settings/dropbox_settings.py”, line 55, in take_backup_to_dropbox did_not_upload, error_log = backup_to_dropbox(upload_db_backup) File “/home/frappe/frappe-bench/apps/frappe/frappe/integrations/doctype/dropbox_settings/dropbox_settings.py”, line 115, in backup_to_dropbox upload_from_folder(get_files_path(is_private=1), 1, “/private/files”, dropbox_client, did_not_upload, error_log) File “/home/frappe/frappe-bench/apps/frappe/frappe/integrations/doctype/dropbox_settings/dropbox_settings.py”, line 133, in upload_from_folder filename = f.file_url.replace(’/private/files/’, ‘’) AttributeError: ‘NoneType’ object has no attribute ‘replace’

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