未定义的变量：类yii2

When I insert this code in gridview, there is error Undefined variable: class

'value' => 'order_customFields_delivery_method',
            'contentOptions' => function ($data)
            {
                if ($data['order_customFields_delivery_method'] == 'Euro')

                {
                    $class = 'style';
                }

                return  [$class => 'font-weight: bold;'];}
        ],

In what can be a problem?

When condition inside if is not met $class is not set but you try to use it anyway.