Rank Math SEO - Fatal Error with HTML Sitemap

Overview of the issue

A fatal error occurs when using the HTML sitemap feature from the Rank Math SEO plugin via a shortcode, [rank_math_html_sitemap].

Fatal error: Uncaught TypeError: Cannot access offset of type string on string in .../wp-content/plugins/wp-seo-multilingual/classes/RankMathSEO/Sitemap/Hooks.php on line 69

Workaround

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

• Edit …/wp-content/plugins/wp-seo-multilingual/classes/RankMathSEO/Sitemap/Hooks.php file.
• Just before line 66:

  1 2 3 4 5 6 7 8 9

  return Obj::assoc(     'loc',     Obj::propOr(         $url['loc'],         (int) Obj::prop( 'ID', $object ),         $this->secondaryHomesById     ),     $url );

• Add this code:

  1 2 3 4 5

  if (!is_array($url)){     $test = $url;     $url = array();     $url['loc'] = $test; }