fix php8 warnings, fixes #1911

Closes #1911

Merge request studip/studip!1255

lib/classes/MyRealmModel.php

@@ -163,8 +163,8 @@ class MyRealmModel
     public static function getCourses($min_sem_key, $max_sem_key, $params = [])
     {
         // init
-        $order_by          = $params['order_by'];
-        $order             = $params['order'];
+        $order_by          = $params['order_by'] ?? null;
+        $order             = $params['order'] ?? null;
         $deputies_enabled  = $params['deputies_enabled'];
 
         $sem_data = Semester::getAllAsArray();
@@ -179,7 +179,7 @@ class MyRealmModel
         }
 
         $semesters = Semester::findMany($semester_ids);
-        $studygroup_filter = !$params['studygroups_enabled'] ? false : true;
+        $studygroup_filter = !empty($params['studygroups_enabled']);
         $ordering          = '';
         // create ordering
         if (!$order_by) {

lib/classes/ResponsiveHelper.php

@@ -195,7 +195,7 @@ class ResponsiveHelper
             $currentIndex = -1;
 
             foreach ($sem_data as $index => $semester) {
-                if ($semester['current']) {
+                if (!empty($semester['current'])) {
                     $currentIndex = $index;
                     break;
                 }

lib/classes/URLHelper.php

@@ -67,7 +67,7 @@ class URLHelper
             return $url;
         }
 
-        if ($url[0] === '/') {
+        if (isset($url[0]) && $url[0] === '/') {
             preg_match('%^[a-z]+://[\w:.-]+%', $base_url, $host);
             $base_url = $host[0] ?? '';
         }

templates/header.php

@@ -287,7 +287,7 @@ if ($navigation) {
             <nav id="navigation-level-2" aria-current="page" aria-label="<?= _('Zweite Navigationsebene') ?>">
 
                 <? if (PageLayout::isHeaderEnabled() /*&& isset($navigation)*/) : ?>
-                    <?= $this->render_partial('tabs', compact('navigation', 'membership')) ?>
+                    <?= $this->render_partial('tabs', compact('navigation')) ?>
                 <? endif; ?>
             </nav>
         <? endif; ?>