code: final public function isInSet($fieldName, $value)
      {
          if (empty($this->data[$fieldName]) || !is_array($this->data[$fieldName])) {
              return false;
          }
  
          if (is_scalar($value) || (is_object($value) && method_exists($value, '__toString'))) {
              $key = trim((string) $value);
          } else {
              return false;
          }
  
          if (0 === strlen($key)) {
              return false;
          }
  
          return isset($this->data[$fieldName][strtolower($key)]);
      }
docs: {@inheritdoc}