public static function normalize($field)
{
$field = wp_parse_args($field, array('js_options' => array(), 'placeholder' => __('Select an item', 'meta-box')));
$field = parent::normalize($field);
$field['js_options'] = wp_parse_args($field['js_options'], array('allowClear' => true, 'width' => 'none', 'placeholder' => $field['placeholder']));
return $field;
}