Throw exception on missing price

[4TT1L4]

Problem:

• In some cases there is no price information available. In such cases the framework returns an empty array.

Solution:

• The framework should not return an array for the current price. It should return a single price point. If there is no price information available then the framework should throw a special exception that could be handled by the client code.

Code:

https://github.com/geniusyield/strategy-executor/blob/f29a01890032b0eaad5f1f33d61d444ec09ea05c/api.py#L69