Yii2如果列表字段为空，如何创建自定义验证器

namespace app\validators;

use yii\validators\Validator;

class EmptyListValidator extends Validator
{
    public function validateAttribute($model, $attribute)
    {
        $value = $model->$attribute;
        
        if (empty($value)) {
            $this->addError($model, $attribute, '列表字段不能为空');
        }
    }
}

public function rules()
{
    return [
        [['listField'], 'app\validators\EmptyListValidator'],
    ];
}