[Closed] Deprecated: rtrim(): Passing null to parameter #1 ($string) PHP 8.1

When WPML Multilingual CMS is active with PHP 8.1 we get this error:

! ) Deprecated: rtrim(): Passing null to parameter #1 ($string) of type string is deprecated in /Users/marcoalmeida/Documents/Websites/_local/wordpress-testing/app/public/wp-includes/formatting.php on line 2786
Call Stack
# Time Memory Function Location
1 0.0022 387136 {main}( ) .../plugins.php:0
2 4.8904 32899312 require_once( '/Users/marcoalmeida/Documents/Websites/_local/wordpress-testing/app/public/wp-admin/admin-header.php ) .../plugins.php:605
3 5.1424 33668208 do_action( $hook_name = 'admin_print_styles' ) .../admin-header.php:132
4 5.1424 33668584 WP_Hook->do_action( $args = [0 => ''] ) .../plugin.php:517
5 5.1424 33668584 WP_Hook->apply_filters( $value = '', $args = [0 => ''] ) .../class-wp-hook.php:332
6 5.1426 33670904 print_admin_styles( '' ) .../class-wp-hook.php:308
7 5.1427 33670904 WP_Dependencies->do_items( $handles = FALSE, $group = ??? ) .../script-loader.php:2213
8 5.1446 33680840 WP_Styles->do_item( $handle = 'colors', $group = FALSE ) .../class-wp-dependencies.php:137
9 5.1446 33680840 WP_Styles->_css_href( $src = TRUE, $ver = '6.3-alpha-55618', $handle = 'colors' ) .../class-wp-styles.php:221
10 5.1446 33680888 apply_filters( $hook_name = 'style_loader_src', $value = '1?ver=6.3-alpha-55618', ...$args = variadic('colors') ) .../class-wp-styles.php:412
11 5.1446 33681296 WP_Hook->apply_filters( $value = '1?ver=6.3-alpha-55618', $args = [0 => '1?ver=6.3-alpha-55618', 1 => 'colors'] ) .../plugin.php:205
12 5.1447 33682104 WPML_Include_Url->filter_include_url( $result = FALSE ) .../class-wp-hook.php:310
13 5.1491 33682776 trailingslashit( $value = NULL ) .../class-wpml-include-url.php:23
14 5.1491 33682776 untrailingslashit( $value = NULL ) .../formatting.php:2771
15 5.1491 33682776 rtrim( $string = NULL, $characters = '/\\' ) .../formatting.php:2786