ValueError: 16 is not in list

Hi，here is the problem when i using BBopt in my project.
`Traceback (most recent call last):`
`File "I:/intention recognition/MyBBopt/testFile.py", line 167, in `
`run_trial()`
` File "I:/intention recognition/MyBBopt/testFile.py", line 81, in run_trial`
`bb.run()`
`File "D:\Anaconda\lib\site-packages\bbopt\optimizer.py", line 255, in run`
`self.run_backend(backend, **options)`
`File "D:\Anaconda\lib\site-packages\bbopt\optimizer.py", line 242, in run_backend`
`self.backend = init_backend(backend, self._examples, self._old_params, *args, **options)`
`File "D:\Anaconda\lib\site-packages\bbopt\backends\hyperopt.py", line 132, in __init__
trial_list = examples_to_trials(examples, params)`
`File "D:\Anaconda\lib\site-packages\bbopt\backends\hyperopt.py", line 103, in examples_to_trials`
`for k, v in zip(sorted(params), make_features(ex["values"], params, fallback_func=lambda name, func, *args, **kwargs: NA, converters={"choice": lambda val, choices: choices.index(val), "randrange": lambda val, start, stop, step: val - start}, convert_fallback=False)):`
`File "D:\Anaconda\lib\site-packages\bbopt\backends\util.py", line 90, in make_features`
`feature = converter_func(feature, *args)`
`File "D:\Anaconda\lib\site-packages\bbopt\backends\hyperopt.py", line 103, in `
`for k, v in zip(sorted(params), make_features(ex["values"], params, fallback_func=lambda name, func, *args, **kwargs: NA, converters={"choice": lambda val, choices: choices.index(val), "randrange": lambda val, start, stop, step: val - start}, convert_fallback=False)):`
`ValueError: 16 is not in list`

i really confused，what's the meaning of 16? it doesn't exist in my project. Could you give me any advice?