How to insert empty option in dropDownListGroup?

Question

Yii

yii framework,
I display the form using yiibiooster.
The form has a select

echo $form->dropDownListGroup(
    $model,
    'parent',
    array(
        'widgetOptions' => array(
            'data' => $category,
            'htmlOptions' => array(),
        ),
    )
);

$category - array of options for slect
How can I print an empty option as well?

Answer 1

Try modifying the $category array itself before outputting. I'm not aware of its structure, but something like:
$category[] = ['value'=>0, 'text'=>''];

Answer 2

Try passing empty=>' ' or 'propt'=> ' ' as an option

Answer 3

I do so. Then, in the model, validation for a non-empty value needs to be done and that's it.

echo $form->dropDownListGroup(
            $model,
            'parent',
            [
                'widgetOptions' => [
                    'data'        => array_merge(array('0' =>'Choose parent'), $category),
                    'htmlOptions' => array(),
                ],
            ]
        );