ERROR: 'NoneType' object is not subscriptable

[virtualbeck]

Seeing this error occur in groups of 4, at a variable frequency from 4-30 mins:

2018/12/04 12:07:37 AM - ERROR: 'NoneType' object is not subscriptable Traceback (most recent call last): File "/.../Crypto-Trading-Bot-master/src/bittrex.py", line 153, in get_historical_data return historical_data["result"][-period:] TypeError: 'NoneType' object is not subscriptable

I ran the program overnight, and the log file has 7600 of these entries.