Adding a comment results in exception

[choules]

When trying to add a comment to a currently running record, kimai-cli crashes with an exception after saving the comment with vi.

ecto-6:kimai-cli choules$ kimai record get-current 
+-------+--------------+------------+------------+------------+-----------+---------+-----------+
|    Id | Start Time   | End Time   | Duration   | Customer   | Project   | Task    | Comment   |
+=======+==============+============+============+============+===========+=========+===========+
| 88403 | 10:30:59     | -          | 0:01       | wycomco    | Internes  | Akquise |           |
+-------+--------------+------------+------------+------------+-----------+---------+-----------+
ecto-6:kimai-cli choules$ kimai record comment 
Id: 88403
Traceback (most recent call last):
  File "/usr/local/bin/kimai", line 11, in <module>
    load_entry_point('kimai-cli==0.6.2', 'console_scripts', 'kimai')()
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/kimai/cli.py", line 481, in comment_on_record
    kimai.comment_on_record(id, comment)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/kimai/kimai.py", line 309, in comment_on_record
    return edit_record(record_id, comment=comment)
  File "/usr/local/Cellar/kimai-cli/0.6.2/libexec/lib/python3.7/site-packages/kimai/kimai.py", line 290, in edit_record
    'end': end.isoformat(),
AttributeError: 'NoneType' object has no attribute 'isoformat'