CakePHP, dependent, multiple fields, validation example

ATable.php

<?php
class ATable extends \Cake\ORM\Table
{
  public function validationDefault(Validator $validator)
  {
    $fields = ['salutation', 'firstname', 'lastname'];
    $validator
      ->provider('allEmptyOrFilled', $fields);

    foreach($fields as $field) {
      $validator
        ->scalar($field)
        ->requirePresence($field, 'create')
        ->allowEmpty($field, function(array $context) {
          return $this->validateAllEmptyOrFilled($context);
        })
        ->add($field, 'allEmptyOrFilled', [
          'rule' => function($value, $context) {
            return !empty($value) && $this->validateAllEmptyOrFilled($context);
          },
          'message' => __('Enter a salutation, firstname and lastname or leave all 3 empty.'),
        ]);
    }
    return $validator;
  }

  protected function countEmptyFields($data, $fields)
  {
    $empty_fields = 0;
    foreach($fields as $field) {
      if(
        is_array($data) && !array_key_exists($field, $data) ||
        !is_array($data) && !isset($data->$field)
      ) {
        return false;
      }
      if(
        is_array($data) && empty($data[$field]) ||
        !is_array($data) && empty($data->$field)
      ) {
        $empty_fields++;
      }
    }
    return $empty_fields;
  }

  public function validateAllEmptyOrFilled($context)
  {
    if(!array_key_exists('allEmptyOrFilled', $context['providers'])) {
      return false;
    }
    $fields = $context['providers']['allEmptyOrFilled'];
    $empty_fields = $this->countEmptyFields($context['data'], $fields);
    return $empty_fields === 0 || $empty_fields === count($fields);
  }
}