ios字典裏面有字典，如何判斷是否有key

認為可以這麽判斷：-(id)handleNullObjectForKey:(NSString *)key {

id object = [self objectForKey:key];

if ([object isKindOfClass:[NSNull class]]) {

return nil;

}

return object;

}

或者是 if ([[dic allKeys] containsObject:key])