#vulnerable code 
                              public Result<AccessToken> refreshAccessToken(String clientId, String clientSecret,
      String grantType, String refreshToken, Boolean wap) {
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    connect.addParameter(params, "client_id", clientId);
    connect.addParameter(params, "client_secret", clientSecret);
    connect.addParameter(params, "grant_type", grantType);
    connect.addParameter(params, "refresh_token", refreshToken);
    String url = "https://graph.qq.com/oauth2.0/token";
    if (Boolean.TRUE.equals(wap)) {
      url = "https://graph.z.qq.com/moc2/token";
    }
    String result = connect.get(url, params);
    String[] results = result.split("\\&");
    JSONObject jsonObject = new JSONObject();
    for (String param : results) {
      String[] keyValue = param.split("\\=");
      jsonObject.put(keyValue[0], keyValue.length > 0 ? keyValue[1] : null);
    }
    String errorCode = jsonObject.optString("code", null);
    if (errorCode != null) {
      jsonObject.put("ret", errorCode);// To match Error.parse()
    }
    return Result.parse(jsonObject, AccessToken.class);
  } 
                            #location 13 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              public Result<AccessToken> refreshAccessToken(String clientId, String clientSecret,
      String grantType, String refreshToken, Boolean wap) {
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    connect.addParameter(params, "client_id", clientId);
    connect.addParameter(params, "client_secret", clientSecret);
    connect.addParameter(params, "grant_type", grantType);
    connect.addParameter(params, "refresh_token", refreshToken);
    String url = "https://graph.qq.com/oauth2.0/token";
    if (Boolean.TRUE.equals(wap)) {
      url = "https://graph.z.qq.com/moc2/token";
    }
    String result = connect.get(url, params);
    return parseAccessTokenResult(result);
  }