Index whether field value is empty or not

<?php

// Replace "CHANGE_ME" with the actual facet _name_

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'CHANGE_ME' == $params['facet_name'] ) {
        if ( '' != $params['facet_value'] ) {
            $params['facet_value'] = 'yes';
            $params['facet_display_value'] = 'Yes';
        }
        else {
            $params['facet_value'] = 'no';
            $params['facet_display_value'] = 'No';
        }
    }
    return $params;
}, 10, 2 );