Custom post theme – thumbnail support

Hi,
I’ve installed latest version of wordpress and tried to create custom post type with thumbnail support:

protected function _applyCustomPostTypes() {
        add_action( 'init', array($this, 'customPostMedia') );
    }

    public function customPostMedia() {
        register_post_type( 'custom-media',
            array(
                'labels' => array(
                    'name' => __( 'Media' ),
                    'singular_name' => __( 'Media' )
                ),
                'public' => true,
                'has_archive' => true,
                'rewrite' => array('slug' => 'custom-media'),
                'supports' => array(
                    'title','editor','thumbnail'
                )

            )
        );
    }

No thumbnail box is shown in add/edit post page for this post type in admin.

How can I add this support ?

Best