Validation radio custom fields on civicrm_validateForm hook does not work
I have a custom field to contact in radio type format, not required field.
I'd like to set up custom error on this empty field by using validateForm but
$fields array doesn't contain a key for this custom field. After setting
$error['custom_xx'] the form is reloaded without displaying the error.
The question is why for Radio type of custom field there is no a key in $fields array?
PS. Related to creating new contact and editing existing contact.