Getting a NoneType Error even though I check for symbol in data.Keys before accessing a Tradebar through data[symbol] inside the for loop.  How can data.Keys work but then data[symbol] be of NoneType?  Running into a huge amount of problems with this platform.  I posted the code, any help understanding this issue would be greatly appreciated.      

Runtime Error: AttributeError : 'NoneType' object has no attribute 'Volume'
at OnData in main.py:line 68
AttributeError : 'NoneType' object has no attribute 'Volume' (Open Stacktrace)