diff --git a/classes/GUI/class.ilTestListTableGUI.php b/classes/GUI/class.ilTestListTableGUI.php
index ff5a3d1..a7a907e 100755
--- a/classes/GUI/class.ilTestListTableGUI.php
+++ b/classes/GUI/class.ilTestListTableGUI.php
@@ -52,7 +52,7 @@ public function __construct(ilObjectGUI $a_parent_obj, $a_parent_cmd)
         /* Pre-configure table */
         $this->setId(
             sprintf(
-                'test_overview_test_list_%d',
+                'xtov_tst_lst_%d',
                 $a_parent_obj->getObject()->getId()
             )
         );
diff --git a/classes/GUI/class.ilTestOverviewTableGUI.php b/classes/GUI/class.ilTestOverviewTableGUI.php
index 8d41db2..6906fa7 100755
--- a/classes/GUI/class.ilTestOverviewTableGUI.php
+++ b/classes/GUI/class.ilTestOverviewTableGUI.php
@@ -404,10 +404,10 @@ private function fetchUserInformation($usr_ids): array
             $user = new ilObjUser();
 
             $user->setId((int)$row['usr_id']);
-            $user->setLogin($row['login']);
-            $user->setUTitle($row['title']);
-            $user->setFirstname($row['firstname']);
-            $user->setLastname($row['lastname']);
+            $user->setLogin((string) $row['login']);
+            $user->setUTitle((string) $row['title']);
+            $user->setFirstname((string) $row['firstname']);
+            $user->setLastname((string) $row['lastname']);
             $user->setFullname();
 
             if (! empty($this->filter['flt_participant_name'])) {
@@ -747,7 +747,7 @@ public function fillHeader(): void
                 include_once("./Services/UIComponent/Tooltip/classes/class.ilTooltipGUI.php");
                 ilTooltipGUI::addTooltip("thc_" . $this->getId() . "_" . $ccnt, $column["tooltip"]);
             }
-            if ((!$this->enabled["sort"] || $column["sort_field"] == "" || $column["is_checkbox_action_column"]) && !$column['link']) {
+            if ((!$this->enabled["sort"] || $column["sort_field"] == "" || $column["is_checkbox_action_column"]) && (!isset($column['link']) || !$column['link'])) {
                 $this->tpl->setCurrentBlock("tbl_header_no_link");
                 if ($column["width"] != "") {
                     $this->tpl->setVariable("TBL_COLUMN_WIDTH_NO_LINK", " width=\"" . $column["width"] . "\"");
@@ -803,7 +803,7 @@ public function fillHeader(): void
             if ($column["class"] != "") {
                 $this->tpl->setVariable("TBL_HEADER_CLASS", " " . $column["class"]);
             }
-            if($column['link']) {
+            if(isset($column['link']) {
                 $this->setExternalLink($column['link']);
             } else {
                 $this->setOrderLink($column["sort_field"], $order_dir);
@@ -844,7 +844,7 @@ protected function buildMemberResultLinkTarget($refId, $activeId): string
         global $ilCtrl;
 
         $link = $ilCtrl->getLinkTargetByClass(
-            array('ilObjTestOverviewGUI', 'ilobjtestgui', 'iltestevaluationgui'),
+            array('ilobjtestgui', 'iltestevaluationgui'),
             'outParticipantsPassDetails'
         );
 
diff --git a/classes/class.ilObjTestOverviewGUI.php b/classes/class.ilObjTestOverviewGUI.php
index f74fde1..10d74d7 100755
--- a/classes/class.ilObjTestOverviewGUI.php
+++ b/classes/class.ilObjTestOverviewGUI.php
@@ -234,8 +234,8 @@ public function initSelectTests(): void
     public function initCourseTests(): void
     {
         $pnode = $this->tree->getParentNodeData((int) $this->request->getQueryParams()['ref_id']);
-        $otype = ilObject::_lookupType($pnode['ref_id'], true); // Parent node is 'crs'
-        $tsts = $this->tree->getFilteredSubTree($pnode['ref_id'], ['tst']);  // and has 'tst's
+        $otype = ilObject::_lookupType((int) $pnode['ref_id'], true); // Parent node is 'crs'
+        $tsts = $this->tree->getFilteredSubTree((int) $pnode['ref_id'], ['tst']);  // and has 'tst's
 
         $refs = [];
         foreach($tsts as $tst) {
@@ -244,7 +244,7 @@ public function initCourseTests(): void
 
         $num_nodes = 0;
         foreach($refs as $ref_id) {
-            if($this->access->checkAccess('tst_statistics', '', $ref_id) || $this->access->checkAccess('write', '', $ref_id)) {
+            if($this->access->checkAccess('tst_statistics', '', (int) $ref_id) || $this->access->checkAccess('write', '', (int) $ref_id)) {
                 $this->object->addTest($ref_id);
                 ++$num_nodes;
             }
diff --git a/classes/mapper/class.ilDataMapper.php b/classes/mapper/class.ilDataMapper.php
index 55e9e5d..960f280 100755
--- a/classes/mapper/class.ilDataMapper.php
+++ b/classes/mapper/class.ilDataMapper.php
@@ -86,7 +86,7 @@ public function getValue(string $table, string $field, array $conditions = array
         $res  = $this->db->query($query);
         $row  = $this->db->fetchObject($res);
 
-        return $row->{strtolower($field)} || $row->{strtoupper($field)} ;
+        return $row !== null ? $row->{strtolower($field)} || $row->{strtoupper($field)} : null;
     }
 
     /**