This is a (multiple allowed):

• bug

• enhancement

• feature-discussion (RFC)

• CakePHP Version: 4.x

there are anomaly between
Cake\Validation\Validator::notEmpty($field, $message = null, $when = false)
and
Cake\Validation\Validator::allowEmpty($field, $when = true, $message = null)

see order of $when and $message
i prefer to ( $field, $when = true, $message = null)