Program: 3039
Project: 3039
Buggy source:
@Override public WxMpPayResult getJSSDKPayResult(String transactionId,String outTradeNo){
  String nonce_str=System.currentTimeMillis() + "String_Node_Str";
  SortedMap<String,String> packageParams=new TreeMap<String,String>();
  packageParams.put("String_Node_Str",wxMpConfigStorage.getAppId());
  packageParams.put("String_Node_Str",wxMpConfigStorage.getPartnerId());
  packageParams.put("String_Node_Str",transactionId);
  packageParams.put("String_Node_Str",outTradeNo);
  packageParams.put("String_Node_Str",nonce_str);
  String sign=WxCryptUtil.createSign(packageParams,wxMpConfigStorage.getPartnerKey());
  String xml="String_Node_Str" + "String_Node_Str" + wxMpConfigStorage.getAppId() + "String_Node_Str"+ "String_Node_Str"+ wxMpConfigStorage.getPartnerId()+ "String_Node_Str"+ "String_Node_Str"+ transactionId+ "String_Node_Str"+ "String_Node_Str"+ outTradeNo+ "String_Node_Str"+ "String_Node_Str"+ nonce_str+ "String_Node_Str"+ "String_Node_Str"+ sign+ "String_Node_Str"+ "String_Node_Str";
  HttpPost httpPost=new HttpPost("String_Node_Str");
  if (httpProxy != null) {
    RequestConfig config=RequestConfig.custom().setProxy(httpProxy).build();
    httpPost.setConfig(config);
  }
  StringEntity entity=new StringEntity(xml,Consts.UTF_8);
  httpPost.setEntity(entity);
  try {
    CloseableHttpResponse response=httpClient.execute(httpPost);
    String responseContent=Utf8ResponseHandler.INSTANCE.handleResponse(response);
    XStream xstream=XStreamInitializer.getInstance();
    xstream.alias("String_Node_Str",WxMpPayResult.class);
    WxMpPayResult wxMpPayResult=(WxMpPayResult)xstream.fromXML(responseContent);
    return wxMpPayResult;
  }
 catch (  IOException e) {
    e.printStackTrace();
  }
  return new WxMpPayResult();
}

Fixed version (ground truth):
@Override public WxMpPayResult getJSSDKPayResult(String transactionId,String outTradeNo){
  String nonce_str=System.currentTimeMillis() + "String_Node_Str";
  SortedMap<String,String> packageParams=new TreeMap<String,String>();
  packageParams.put("String_Node_Str",wxMpConfigStorage.getAppId());
  packageParams.put("String_Node_Str",wxMpConfigStorage.getPartnerId());
  if (transactionId != null && !"String_Node_Str".equals(transactionId.trim()))   packageParams.put("String_Node_Str",transactionId);
 else   if (outTradeNo != null && !"String_Node_Str".equals(outTradeNo.trim()))   packageParams.put("String_Node_Str",outTradeNo);
 else   throw new IllegalArgumentException("String_Node_Str");
  packageParams.put("String_Node_Str",nonce_str);
  packageParams.put("String_Node_Str",WxCryptUtil.createSign(packageParams,wxMpConfigStorage.getPartnerKey()));
  StringBuilder request=new StringBuilder("String_Node_Str");
  for (  Entry<String,String> para : packageParams.entrySet()) {
    request.append(String.format("String_Node_Str",para.getKey(),para.getValue(),para.getKey()));
  }
  request.append("String_Node_Str");
  HttpPost httpPost=new HttpPost("String_Node_Str");
  if (httpProxy != null) {
    RequestConfig config=RequestConfig.custom().setProxy(httpProxy).build();
    httpPost.setConfig(config);
  }
  StringEntity entity=new StringEntity(request.toString(),Consts.UTF_8);
  httpPost.setEntity(entity);
  try {
    CloseableHttpResponse response=httpClient.execute(httpPost);
    String responseContent=Utf8ResponseHandler.INSTANCE.handleResponse(response);
    XStream xstream=XStreamInitializer.getInstance();
    xstream.alias("String_Node_Str",WxMpPayResult.class);
    WxMpPayResult wxMpPayResult=(WxMpPayResult)xstream.fromXML(responseContent);
    return wxMpPayResult;
  }
 catch (  IOException e) {
    throw new RuntimeException("String_Node_Str",e);
  }
}