Here is my code :

```
$model->free = true;
echo $form->field($model, 'free', ['inputOptions'=>['class'=>'form-control input-lg ']])->checkbox();

```

What I want is if the user doesn't uncheck, the default value must be sent to the server but my surprise, it is sending $model->free to the server null whether the user unchecks or leaves it as it is; to send the checked value, the user has to uncheck and check which stress.

How can I achieve what I want?