public function getAttributeValue($sku, $key) {
    $id = $sku instanceof SKUInterface ? $sku->id() : $sku;

    $query = \Drupal::database()->select('acm_sku__attributes', 'acm_sku__attributes');
    $query->addField('acm_sku__attributes', 'attributes_value');
    $query->condition("acm_sku__attributes.entity_id", $id);
    $query->condition("acm_sku__attributes.attributes_key", $key);
    return $query->execute()->fetchField();
  }