facetwp facet orderby combine rules with FIELD

<?php 
/** multiple facetwp_facet_orderby rules **/
add_filter( 'facetwp_facet_orderby', function( $orderby, $facet ) {
    if ( 'source' == $facet['name'] ) {
        $orderby = 'FIELD( f.facet_display_value, "Second Value in Dropdown", "First Value in Dropdown" ) DESC, f.facet_display_value ASC';
    }
    return $orderby;
}, 11, 2 );