NSNull

从JSon中传过来的数据

ID = 6;
currentStatus = "Assert Demand";
driver = ;
fromAddress = Belgooly;
fromLat = 51.7360386044182;
fromLon = -8.48393440246582;
pin = ;
seat = 3;
startTime = -2147484000;
toAddress = KCP;
toLat = 51.7094938361641;
toLon = -8.51498365402222;
vehicle = ;
如何判断为
用［NSNull null］判断