fix errors and warnings, closes #3831

Closes #3831

Merge request studip/studip!2695

lib/classes/Seminar.class.php

@@ -1611,10 +1611,6 @@ class Seminar
         $statement = DBManager::get()->prepare($query);
         $statement->execute([$s_id]);
 
-        $query = "DELETE FROM wiki_locks WHERE range_id = ?";
-        $statement = DBManager::get()->prepare($query);
-        $statement->execute([$s_id]);
-
         // delete course config values
         ConfigValue::deleteBySQL('range_id = ?', [$s_id]);
 

lib/modules/CoreWiki.class.php

@@ -183,7 +183,8 @@ class CoreWiki extends CorePlugin implements StudipModule
      */
     public static function getTOC($startPage, $active_title = null): TOCItem
     {
-        $root = new TOCItem($startPage->isNew() || $startPage->name === 'WikiWikiWeb'
+        $root = new TOCItem(
+            ($startPage && ($startPage->isNew() || $startPage->name === 'WikiWikiWeb'))
             ? _('Wiki-Startseite')
             : $startPage->name
         );