Random issue on import

When importing it sometimes spew an error which doesn't seems to impact import?

root@api:/app# python manage.py import_files "/music/Activate*/**.mp3" --recursive --noinput --no-acoustid /usr/local/lib/python3.5/site-packages/psycopg2/__init__.py:144: UserWarning: The psycopg2 wheel package will be renamed from release 2.8; in order to keep installing from binary please use "pip install psycopg2-binary" instead. For details see: <http://initd.org/psycopg/docs/install.html#binary-install-from-pypi>. """) This will import 9 files matching this pattern: /music/Activate*/**.mp3 Successfully imported 9 tracks For details, please refer to import batch #8 Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0x7fa0408dfb70> Traceback (most recent call last): File "/usr/local/lib/python3.5/weakref.py", line 117, in remove TypeError: 'NoneType' object is not callable Exception ignored in: <function WeakValueDictionary.__init__.<locals>.remove at 0x7fa0408dfb70> Traceback (most recent call last): File "/usr/local/lib/python3.5/weakref.py", line 117, in remove TypeError: 'NoneType' object is not callable root@api:/app#