message: Use hasParam() instead of checking server.arg() for NULL, it returns a String anyway.
  Don't use .c_str() when its being assigned to a String anyway
diff: @@ -1228,9 +1228,13 @@ void WiFiManager::doParamSave(){
  break;
  }
  //read parameter from server
  + String name = (String)FPSTR(S_parampre)+(String)i;
  String value;
  - if(server->arg((String)FPSTR(S_parampre)+(String)i) != NULL) value = server->arg((String)FPSTR(S_parampre)+(String)i).c_str();
  - else value = server->arg(_params[i]->getID()).c_str();
  + if(server->hasArg(name)) {
  + value = server->arg(name);
  + } else {
  + value = server->arg(_params[i]->getID());
  + }
  //store it in params array
  value.toCharArray(_params[i]->_value, _params[i]->_length+1); // length+1 null terminated
  