I have created fields group with only one field in it.
Form with it doesn’t save this field value :/

Should I change something in my field definition?

piklist('field', array(
    'type' => 'group'
    ,'field' => 'notifications_settings'
    ,'label' => __('Notifications', 'pgx-application-form')
    ,'scope' => 'option'
    ,'position' => 'start'
    ,'fields' => array(
        array(
            'type' => 'text'
            ,'field' => 'notification_email'
            ,'template' => 'form_table_inline_description'
            ,'label' => 'Email'
            ,'attributes' => array(
                'class' => 'regular-text'
            )
        )
    )
));