cannnot provide negative values to the apply_threshold script

Here is what I have tried so far:

bin/bob_apply_threshold.py "-0.4221387" ~/nonorm/scores-dev
Usage: bob_apply_threshold.py [-v...] [options] <threshold> <scores>
       bob_apply_threshold.py --help
       bob_apply_threshold.py --version
bin/bob_apply_threshold.py '-0.4221387' ~/nonorm/scores-dev
Usage: bob_apply_threshold.py [-v...] [options] <threshold> <scores>
       bob_apply_threshold.py --help
       bob_apply_threshold.py --version
bin/bob_apply_threshold.py "'-0.4221387'" ~/nonorm/scores-dev
cannot convert '-0.4221387' into float for threshold
Usage: bob_apply_threshold.py [-v...] [options] <threshold> <scores>
       bob_apply_threshold.py --help
       bob_apply_threshold.py --version
bin/bob_apply_threshold.py -- -0.4221387 ~/nonorm/scores-dev
Usage: bob_apply_threshold.py [-v...] [options] <threshold> <scores>
       bob_apply_threshold.py --help
       bob_apply_threshold.py --version