IndexError: index 0 is out of bounds for axis 0 with size 0

[rkuo2000]

Python 3.6.3, tensorflow-1.4.0 on Windows 7 Ultimate SP1
python main.py --dataset ptb
self.loader = BatchLoader(self.data_dir, self.dataset_name, self.batch_size, self.seq_length, self.max_word_length)
File "C:\Users\akuo\lstm-char-cnn-tensorflow\batch_loader.py", line 52, in init
ydata[-1] = data[0].copy()
IndexError: index 0 is out of bounds for axis 0 with size 0

there are quite a few -1 in batch_loader.py, should I replace them all to 0 ?