Performance evaluation is broken

[leondz]

Calling run_tagger with -p breaks:

Traceback (most recent call last):
  File "./run_tagger.py", line 124, in <module>
    print("\n", er.bio_classification_report(y, y_hat))
  File "/home/leon/Dropbox/dev/entity_recognition/er.py", line 88, in bio_classification_report
    digits=4,
  File "/usr/local/lib/python3.4/dist-packages/sklearn/metrics/classification.py", line 1234, in classification_report
    width = max(len(cn) for cn in target_names)
ValueError: max() arg is an empty sequence
leon@t430:~/dev/entity_recognition$