Google XML Sitemaps - PHP Warning: preg_match(): Unknown modifier...

Overview of the issue

Under some scenarios, you may encounter a PHP warning like the following, particularly if you are using Google XML Sitemaps plugin alongside our system

Warning: preg_match(): Unknown modifier '-' in /wp-content/plugins/sitepress-multilingual-cms/inc/absolute-links/absolute-links.class.php on line 186

Workaround

Please, make sure of having a full backup of your site before proceeding.

• Open …/wp-content/plugins/sitepress-multilingual-cms/inc/absolute-links/absolute-links.class.php file.
• Look for line 186.
• Replace:

  if ( preg_match( "!^$match!", $request_match, $matches ) || preg_match( "!^$match!", urldecode( $request_match ), $matches ) ) {
  

• With:

  if ( preg_match( "~^$match~", $request_match, $matches ) || preg_match( "~^$match~", urldecode( $request_match ), $matches ) ) {