code: protected Map<String, String> filterSignParams(final Map<String, ?> params) {
          Map<String, String> validParams = new TreeMap<>();
  
          for (Map.Entry<String, ?> param : params.entrySet()){
              if (WepayField.SIGN.equals(param.getKey())
                      || param.getValue() == null
                      || "".equals(String.valueOf(param.getValue()))){
                  continue;
              }
              validParams.put(param.getKey(), String.valueOf(param.getValue()));
          }
  
          return validParams;
      }
docs: 过滤签名参数(升序，排出空值，sign)
  @param params 待校验参数
  @return 过滤后的参数