Traceback (most recent call last):


 "/usr/local/lib/python3.6/dist-packages/optuna/study.py", line 709, in _run_trial

result = func(trial)


 "/usr/local/lib/python3.6/dist-packages/optuna/integration/_lightgbm_tuner/optimize.py", line 302, in __call__

cv_results = lgb.cv(self.lgbm_params, self.train_set, **self.lgbm_kwargs)


 "/usr/local/lib/python3.6/dist-packages/lightgbm/engine.py", line 576, in cv

evaluation_result_list=res))


 "/usr/local/lib/python3.6/dist-packages/lightgbm/callback.py", line 221, in _callback

_init(env)


 "/usr/local/lib/python3.6/dist-packages/lightgbm/callback.py", line 191, in _init

raise ValueError('For early stopping, '
ValueError: For early stopping, at least one dataset and eval metric is required for evaluation

Traceback (most recent call last):


 "calibre\db\cache.py", line 1395, in set_metadata


 "calibre\db\cache.py", line 1318, in set_cover


 "calibre\db\backend.py", line 1500, in set_cover


 "calibre\utils\img.py", line 285, in save_cover_data_to


 "calibre\utils\img.py", line 197, in image_to_data
ValueError: Failed to export image as JPEG with error: Image is empty
