FacetWP - force no results when proximity is empty

functions.php

<?php

// Add to your (child) theme's functions.php

add_filter( 'facetwp_pre_filtered_post_ids', function( $post_ids, $class ) {
    $facet_name = 'senior_living_proximity';

    if ( empty( $class->facets[ $facet_name ]['selected_values'] ) ) {
        $post_ids = [ 0 ]; // force a 0-filled (empty) array
    }

    return $post_ids;
}, 10, 2 );