Program: 21504
Project: 21504
Buggy source:
@Override public boolean interact(){
  logger.info("String_Node_Str");
  String ipBefore;
  String ipAfter;
  RouterData routerData=configuration.getRouterData();
  String routerIP=configuration.getRouterIP();
  String routerUsername=configuration.getRouterUsername();
  String routerPassword=configuration.getRouterPassword();
  int routerPort=configuration.getRouterPort();
  String login=routerData.getLogin();
  String disconnect=routerData.getDisconnect();
  String connect=routerData.getConnect();
  if (routerUsername != null && routerPassword != null)   Authenticator.setDefault(new InternalAuthenticator(routerUsername,routerPassword));
  String routerPage;
  if (routerPort <= 0)   routerPage="String_Node_Str" + routerIP + "String_Node_Str";
 else   routerPage="String_Node_Str" + routerIP + "String_Node_Str"+ routerPort+ "String_Node_Str";
  RequestInfo requestInfo=null;
  ipBefore=getIPAddress(routerPage,routerData);
  logger.fine("String_Node_Str" + ipBefore);
  if (login != null && !login.equals("String_Node_Str")) {
    login.replaceAll(VAR_USERNAME,routerUsername);
    login.replaceAll(VAR_PASSWORD,routerPassword);
    requestInfo=doThis("String_Node_Str",routerPage + login,requestInfo,routerData.getLoginRequestProperties(),routerData.getLoginPostParams(),routerData.getLoginType());
    if (requestInfo == null || !requestInfo.isOK()) {
      logger.severe("String_Node_Str" + requestInfo.getResponseCode());
      return false;
    }
  }
  requestInfo=doThis("String_Node_Str",routerPage + disconnect,requestInfo,routerData.getDisconnectRequestProperties(),routerData.getDisconnectPostParams(),routerData.getDisconnectType());
  if (requestInfo == null || !requestInfo.isOK()) {
    logger.severe("String_Node_Str" + requestInfo.getResponseCode());
    return false;
  }
  logger.fine("String_Node_Str");
  requestInfo=doThis("String_Node_Str",connect,null,null,null,RouterData.TYPE_WEB_GET);
  if (requestInfo == null || !requestInfo.isOK()) {
    logger.severe("String_Node_Str" + requestInfo.getResponseCode());
    return false;
  }
  ipAfter=getIPAddress(routerPage,routerData);
  logger.fine("String_Node_Str" + ipAfter);
  if (ipBefore == null || ipAfter == null || ipBefore.equals(ipAfter)) {
    logger.severe("String_Node_Str");
    return false;
  }
  return true;
}

Fixed version (ground truth):
@Override public boolean interact(){
  configuration=JDUtilities.getConfiguration();
  logger.info("String_Node_Str");
  String ipBefore;
  String ipAfter;
  RouterData routerData=configuration.getRouterData();
  String routerIP=configuration.getRouterIP();
  String routerUsername=configuration.getRouterUsername();
  String routerPassword=configuration.getRouterPassword();
  int routerPort=configuration.getRouterPort();
  String login=routerData.getLogin();
  String disconnect=routerData.getDisconnect();
  String connect=routerData.getConnect();
  if (routerUsername != null && routerPassword != null)   Authenticator.setDefault(new InternalAuthenticator(routerUsername,routerPassword));
  String routerPage;
  if (routerPort <= 0)   routerPage="String_Node_Str" + routerIP + "String_Node_Str";
 else   routerPage="String_Node_Str" + routerIP + "String_Node_Str"+ routerPort+ "String_Node_Str";
  RequestInfo requestInfo=null;
  ipBefore=getIPAddress(routerPage,routerData);
  logger.fine("String_Node_Str" + ipBefore);
  if (login != null && !login.equals("String_Node_Str")) {
    login.replaceAll(VAR_USERNAME,routerUsername);
    login.replaceAll(VAR_PASSWORD,routerPassword);
    requestInfo=doThis("String_Node_Str",routerPage + login,requestInfo,routerData.getLoginRequestProperties(),routerData.getLoginPostParams(),routerData.getLoginType());
    if (requestInfo == null) {
      logger.severe("String_Node_Str");
      return false;
    }
 else     if (!requestInfo.isOK()) {
      logger.severe("String_Node_Str" + requestInfo.getResponseCode());
      return false;
    }
  }
  requestInfo=doThis("String_Node_Str",routerPage + disconnect,requestInfo,routerData.getDisconnectRequestProperties(),routerData.getDisconnectPostParams(),routerData.getDisconnectType());
  if (requestInfo == null) {
    logger.severe("String_Node_Str");
    return false;
  }
 else   if (!requestInfo.isOK()) {
    logger.severe("String_Node_Str" + requestInfo.getResponseCode());
    return false;
  }
  logger.fine("String_Node_Str");
  requestInfo=doThis("String_Node_Str",connect,null,null,null,RouterData.TYPE_WEB_GET);
  if (requestInfo == null) {
    logger.severe("String_Node_Str");
    return false;
  }
 else   if (!requestInfo.isOK()) {
    logger.severe("String_Node_Str" + requestInfo.getResponseCode());
    return false;
  }
  ipAfter=getIPAddress(routerPage,routerData);
  logger.fine("String_Node_Str" + ipAfter);
  if (ipBefore == null || ipAfter == null || ipBefore.equals(ipAfter)) {
    logger.severe("String_Node_Str");
    return false;
  }
  return true;
}