這個方法把<null>轉為空字串

-(void)setValuesForKeysWithDictionary:(NSDictionary<NSString *,id> *)keyedValues

{

NSMutableDictionary *dic = [[NSMutableDictionaryalloc] initWithDictionary:keyedValues];

    NSArray *valueArray= [dic allKeys];

    for (NSString *key in valueArray) {

        if ([[dic objectForKey

                [dic setObject:@"" forKey:key];

        }

    }

    [supersetValuesForKeysWithDictionary:dic];

}