Dangerous nulls in AttributeExtractor

[prmr]

In AttributeExtractor methods getAttributesForCategory and getAttributesForCategory you pass the result of a HashMap.get directly into a unmodifiableList. This is dangerous because the get call has null in its valid range. You should decide how to handle invalid categories (I recommend a runtime exception) and adjust the logic so it's impossible to pass a null into unmodifiableList.

[asutcl]

I will try to take a look at this before class.

[asutcl]

Would returning an empty list and Logging an error be an acceptable solution?

[prmr]

I think it's ok, as long as the contract is clear.