Errors in indexmenu plugin after upgrade to kaos 6a

[macin]

Hi, I keep getting a lot of errors like these:

#0 /var/www/html/lib/plugins/indexmenu/syntax/indexmenu.php(842): dokuwiki\ErrorHandler::errorHandler(2, '...', '...', 842)
#1 /var/www/html/inc/html.php(500): syntax_plugin_indexmenu_indexmenu->formatIndexmenuItem(Array)
#2 /var/www/html/lib/plugins/indexmenu/syntax/indexmenu.php(544): html_buildlist(Array, '...', Array, Array)
#3 /var/www/html/lib/plugins/indexmenu/syntax/indexmenu.php(531): syntax_plugin_indexmenu_indexmenu->buildNoJSTree(Array, '...', '...')
#4 /var/www/html/lib/plugins/indexmenu/syntax/indexmenu.php(466): syntax_plugin_indexmenu_indexmenu->buildHtmlIndexmenu('...', Array, Array, Array, 1)
#5 /var/www/html/lib/plugins/text/renderer.php(45): syntax_plugin_indexmenu_indexmenu->render('...', Object(renderer_plugin_text), Array)
#6 /var/www/html/inc/parserutils.php(691): renderer_plugin_text->plugin('...', Array, 5, '...')
#7 /var/www/html/inc/parserutils.php(158): p_render('...', Array, NULL)
#8 /var/www/html/lib/plugins/searchtext/action.php(34): p_cached_output('...', '...')
#9 /var/www/html/inc/Extension/EventHandler.php(80): action_plugin_searchtext->_getSearch(Object(dokuwiki\Extension\Event), NULL)
#10 /var/www/html/inc/Extension/Event.php(75): dokuwiki\Extension\EventHandler->process_event(Object(dokuwiki\Extension\Event), '...')
#11 /var/www/html/inc/indexer.php(189): dokuwiki\Extension\Event->advise_before()
#12 /var/www/html/inc/TaskRunner.php(206): idx_addPage('...', true)
#13 /var/www/html/inc/TaskRunner.php(52): dokuwiki\TaskRunner->runIndexer()
#14 /var/www/html/lib/exe/taskrunner.php(20): dokuwiki\TaskRunner->run()
#15 {main}

All seems to be working, but this errors is constanly repeated in the logs. Could you please advice what should I do?

Here is what I used to configure the indexmenu:

{{indexmenu>..#1|js#template.png context navbar msort nsort tsort}}