uncaught exception: join(): Argument #2 ($array) must be of type ?array, string given

in file: /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php line 834
#0 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(834): join()
#1 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/lib/php/Boot.class.php(853): _hx_build_paths()
#2 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/lib/com/wiris/system/CallWrapper.class.php(44): require_once('...')
#3 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/plugin.php(5): com_wiris_system_CallWrapper->init()
#4 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/pluginbuilder.php(3): require_once('...')
#5 /home/etrapez/www/wp-includes/js/tinymce/plugins/tiny_mce_wiris/integration/showimage.php(5): require_once('...')
#6 {main}