required attribute not working

[Biswajit Maity]

$cmb->add_field( array(
	'name'    => __( 'Check', 'cmb2' ),
	'id'      => $prefix . 'type',
	'type'    => 'select',
	'options' => array(
		'type1' => __( 'Type 1', 'cmb2' ),
		'type2' => __( 'Type 2', 'cmb2' ),
		'type3' => __( 'Type 3', 'cmb2' ),
	),
	'attributes' => array(
		'required'            => true
	),
	'default' => 'type1',
) );

$cmb->add_field( array(
	'name'       => 'Thumbnail',
	'id'         => $prefix . 'thumb',
	'type'    => 'file',
	'options' => array(
		'url' => false,
	),
	'text'    => array(
		'add_upload_file_text' => 'Add Thumbnail'
	),
	'query_args' => array(
		'type' => array(
			'image/gif',
			'image/jpeg',
			'image/png',
		),
	),
	'preview_size' => 'thumbnail',
	'attributes' => array(
		'required'            => true,
		'data-conditional-id' => $prefix . 'type',
		'data-conditional-value' => wp_json_encode( array( 'type1', 'type2') ),
	),

) );

$cmb->add_field( array(
	'name'       => 'PDF',
	'id'         => $prefix . 'pdf',
	'type'    => 'file',
	'options' => array(
		'url' => false,
	),
	'text'    => array(
		'add_upload_file_text' => 'Add PDF'
	),
	'query_args' => array(
		'type' => 'application/pdf',
	),
	'attributes' => array(
		'required'            => true,
		'data-conditional-id'    => $prefix . 'type',
		'data-conditional-value' => 'type3',
	),
) );