Parsing fix


The problem boils down to not being able to store nil in an NSDictionary. That sounds like something that ought to be possible, but a lot of people are saying you can't-- but in either case, NSJsoneWhatever serializes things that look like null to the string literal @"<null>". Rather than looping through each response and copying the dictionary with values we expect, I made a macro to compare a value against all the possible null-ish patterns. 

Try to remember to use that for all response dictionaries in the future when checking for null.