Fix for defect where on iOS versions greater than 6, viewing an unnamed pin would cause a crash. This was a result of serializing empty strings with RapidJson. On iOS 6 and below, empty strings come in from the UI as 'nil' whereas on iOS 7 and above, they come in as non-null strings of length zero. We need to detect the nil-or-empty case and handle both by using the placeholder. Fix tested on iOS 7 iPad2 simulator and iOS 6 iPad2 device.