When running the beat command line utility to perform one of the following operations (indexing or viewing database content), the script crashes with such an error:

./bin/beat --prefix=work db view atnt/1/idiap/train
Traceback (most recent call last):
  File "./bin/beat", line 34, in <module>
    sys.exit(beat.cmdline.scripts.beat.main())
  File "/remote/idiap.svm/user.active/tpereira/BEAT/beat.core/src/beat.cmdline/beat/cmdline/scripts/beat.py", line 160, in main
    return module.process(args)
  File "/remote/idiap.svm/user.active/tpereira/BEAT/beat.core/src/beat.cmdline/beat/cmdline/databases.py", line 400, in process
    return view_output(args['config'], args['<set_name>'])
  File "/remote/idiap.svm/user.active/tpereira/BEAT/beat.core/src/beat.cmdline/beat/cmdline/databases.py", line 330, in view_output
    input_group = view.input_group(exclude_outputs=excluded_outputs)
  File "/remote/idiap.svm/user.active/tpereira/BEAT/beat.core/beat/core/database.py", line 146, in input_group
    for output in self.outputs:
TypeError: 'NoneType' object is not iterable