Cannot find custom logo

[glesbygdn]

Warning: Trying to access array offset on value of type bool in /wp-content/plugins/headless-cms/inc/classes/api/class-header-footer-api.php on line <i>139</i>

PHP 8.0, Wordpress 5.8:

public function get_custom_logo_url( $key ) {
    $custom_logo_id = get_theme_mod( $key );
    $image          = wp_get_attachment_image_src( $custom_logo_id, 'full' );
    return $image[0];
}