-[__NSDictionaryM urlEncodedKeyValueString]: unrecognized selector sent to instance

[cczufish]

NSDictionary *pDic = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:1], @"userId", [NSNumber numberWithInt:1], @"skuId", nil];

if (([method isEqualToString:@"GET"] || [method isEqualToString:@"DELETE"]) && (params && [params count] > 0)) {

  finalURL = [NSURL URLWithString:[NSString stringWithFormat:@"%@?%@", aURLString,
                                   [self.fieldsToBePosted urlEncodedKeyValueString]]];
}

-[__NSDictionaryM urlEncodedKeyValueString]: unrecognized selector sent to instance 0x170e4ec40