Based on Apple Document Here, we can use the following two methods to compare Boolean:
NSPredicate *newPredicate = [NSPredicate predicateWithFormat:@"anAttribute == %@",[NSNumber numberWithBool:aBool]];
NSPredicate *testForTrue = [NSPredicate predicateWithFormat:@"anAttribute == YES"];
However, the above predicate cannot get out the ones with empty anAttribute. To deal with an empty attribute, you need the following method according to Apple document here:
predicate = [NSPredicate predicateWithFormat:@"firstName = nil"]; // it's in the document
or
predicate = [NSPredicate predicateWithFormat:@"firstName == nil"]; // == and = are interchangeable here