If I understood you correctly:
I ask you if it is Day or Night and you say it’s 7pm. Which doesn’t really solve my question of whether it is day or night but, if I add a few lines of logic I can predict with enough accuracy that in the location i am at at that exact time it would be night today (but maybe not other day)
Now that you read that text, does it seem good to return “None” when you are 100% expecting a Possitive float? It would make more sense to me to return a negative number to define a state like this address does not even have a record of this coin instead of returning None as a balance.
I do believe it is important to tell that an address has have no such token, but returning something other than a number for a balance seems just wrong.