code: private boolean isNull(Field field, Object obj) {
      try {
        if (!field.isAccessible()) {
          field.setAccessible(true);
        }
        return field.get(obj) == null;
      } catch (Exception e) {
        e.printStackTrace();
      }
  
      return false;
    }
docs: 列名判空处理
  
  @param field
  @return boolean