lucasmedeirosleite/EasyMapping — pull request #11 by chrisalbert (2013-05-17 16:42:40+00:00)
Title: Fixed crash when representation contains date field with value [NSNull null]

As described in the title, EKTransformer expects NSString for ```transformString:withDateFormat:```. EKMapper doesn't check the value contained in the representation before calling this method, leading to a crash if the value is [NSNull null].

This commit fixes this by checking if the value is an NSString. If not, nil is returned.