POS Tagging Example Not Working

[Sophylax]

When trying to run the POS Tagging Example experiment, I get the following exception:

Traceback (most recent call last):
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/params.py", line 211, in pop
    value = self.params.pop(key)
KeyError: 'metric_input_handler'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/sophylax/anaconda3/envs/trapper/bin/trapper", line 8, in <module>
    sys.exit(run())
  File "/home/sophylax/Documents/Git/Github/trapper/trapper/__main__.py", line 12, in run
    main(prog="trapper")
  File "/home/sophylax/Documents/Git/Github/trapper/trapper/commands.py", line 178, in main
    args.func(args)
  File "/home/sophylax/Documents/Git/Github/trapper/trapper/commands.py", line 101, in run_experiment_from_args
    run_experiment(args.config_path, args.overrides)
  File "/home/sophylax/Documents/Git/Github/trapper/trapper/training/train.py", line 41, in run_experiment
    return _run_experiment_from_params(params)
  File "/home/sophylax/Documents/Git/Github/trapper/trapper/training/train.py", line 64, in _run_experiment_from_params
    trainer = TransformerTrainer.from_params(params)
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/from_params.py", line 608, in from_params
    **extras,
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/from_params.py", line 636, in from_params
    kwargs = create_kwargs(constructor_to_inspect, cls, params, **extras)
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/from_params.py", line 207, in create_kwargs
    cls.__name__, param_name, annotation, param.default, params, **extras
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/from_params.py", line 310, in pop_and_construct_arg
    popped_params = params.pop(name, default) if default != _NO_DEFAULT else params.pop(name)
  File "/home/sophylax/anaconda3/envs/trapper/lib/python3.7/site-packages/allennlp/common/params.py", line 216, in pop
    raise ConfigurationError(msg)
allennlp.common.checks.ConfigurationError: key "metric_input_handler" is required