Changed `""` into `''` to pass an empty token. Seems to be linked to this warning:
```
/opt/conda/lib/python3.8/site-packages/traitlets/traitlets.py:2195: FutureWarning: Supporting extra quotes around Unicode is deprecated in traitlets 5.0. Use '' instead of "''" – or use CUnicode.
```
Added debug information (ouput of the command line).
- If NB_GID is set, it is likely that files created should have NB_GID
as their gid (if it doesn't matter, then this change is irrelevant.
If it does matter, the liklihood that 100 matches with what the user
wants is low).
- When NB_GID is set, create a new group with that gid. Then, set
this as the primary gid of the user. Set the user's supplemental
gids to NB_GID,100.