--log option does not work in the evaluate command

See:

bin/bob measure evaluate measure_scores/scores-{dev,eval} -e -l /tmp/log.txt
Traceback (most recent call last):
  File "bin/bob", line 29, in <module>
    sys.exit(bob.extension.scripts.main_cli())
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/amir/idiap/git/bobs/bob.pad.base/src/bob.measure/bob/measure/script/commands.py", line 258, in evaluate
    ctx.invoke(metrics, scores=scores, evaluation=evaluation)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/amir/miniconda/envs/bob36/lib/python3.6/site-packages/click/decorators.py", line 17, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/amir/idiap/git/bobs/bob.pad.base/src/bob.measure/bob/measure/script/commands.py", line 41, in metrics
    process = figure.Metrics(ctx, scores, evaluation, load.split)
  File "/home/amir/idiap/git/bobs/bob.pad.base/src/bob.measure/bob/measure/script/figure.py", line 170, in __init__
    self.log_file = open(self._log, self._open_mode)
TypeError: open() argument 2 must be str, not None