Json NSManagedObject 属性值的 NSNull 处理

I'm setting values for properties of my NSManagedObject, these values are coming from a NSDictionary properly serialized from a JSON file. My problem is, that, when some value is [NSNull null], I can't assign directly to the property:

    fight.winnerID = [dict objectForKey:@"winner"];

this throws a NSInvalidArgumentException

"winnerID"; desired type = NSString; given type = NSNull; value = <null>;

我可以很容易地判断[NSNull null]的值，然后指定nil:

fight.winnerID = [dict objectForKey:@"winner"] == [NSNull null] ? nil : [dict objectForKey:@"winner"];

But I think this is not elegant and gets messy with lots of properties to set.

此外，在处理NSNumber处房产时，这会变得更加困难:

fight.round = [NSNumber numberWithUnsignedInteger:[[dict valueForKey:@"round"] unsignedIntegerValue]]

The NSInvalidArgumentException is now:

[NSNull unsignedIntegerValue]: unrecognized selector sent to instance

In this case I have to treat [dict valueForKey:@"round"] before making an NSUInteger value of it. And the one line solution is gone.

我试着制作一个@try@catch块，但是一旦捕捉到第一个值，它就会跳过整个@try块，并且忽略下一个属性.

有没有更好的方法来处理[NSNull null]个问题，或者让这完全不同但更简单？