code: protected function setFileFieldValue($value)
      {
          if (version_compare(PHP_VERSION, '5.5.0') >= 0){
              if (!($value instanceof \CURLFile)){
                  $value = ltrim($value,"@");
                  $value = new \CURLFile($value);
              }
          } else {
              if (strpos($value, '@') !== 0) {
                  $value = '@'.$value;
              }
          }
          return $value;
      }
docs: Configure the filepath to have an @ symbol in front if one is not found
  @param string $value
  @return string