title: NSComparisonPredicate to find empty strings
body: <p>I need to check if a string in my array is empty using the NSComparisonPredicate. The predicate that is being executed is:    string MATCHES[c] ""
  But nothing shows up in the results, it does not list my empty strings.
  Is my predicate wrong or there is just another way of dealing with empty strings with NSPredicate?</p>