extractString static method
Implementation
static Map<String, String> extractString(Map<String, Object?> form,
    [bool allowEmpty = false]) {
  var extraData = <String, String>{};
  form.forEach((key, value) {
    if (value is Map<String, Object?>) {
      if (!allowEmpty && (value['value'] == null || value['value'] == '')) {
        return;
      }
      extraData[key] = value['value']?.toString() ?? '';
    }
  });
  return extraData;
}