在c++中，得到一个错误，说“std: string {aka std::basic_string}”不是从“const __gnu_cxx::__normal_iterator<_IteratorL， _Container>”派生出来的。

int webServerPort = -1;    

void configure(std::string responseFile, callback_function call_back, std::string urlRegex = NULL) {
        std::string url = "https://0.0.0.0:" + webServerPort + "fake_settings/?file=" + responseFile;
        if(urlRegex != NULL) {  // GOT ERROR HERE
            url += "&pattern=" + urlRegex;
        }
int webServerPort = -1;    

void configure(std