prevent warnings, fixes #2549

Closes #2549

Merge request studip/studip!1724

app/views/admin/install/layout.php

@@ -59,14 +59,14 @@
                 ) ?>
             <?php endif; ?>
 
-            <?php if (!$valid && $button_label): ?>
+            <?php if (!$valid && !empty($button_label)): ?>
                 <?= Studip\Button::create($button_label, 'continue') ?>
             <?php elseif (!$valid): ?>
                 <?= Studip\Button::create(_('Erneut prüfen'), 'check') ?>
             <?php elseif ($next_step): ?>
                 <?= Studip\Button::create($button_label ?? (_('Weiter') . ' >>'), 'continue') ?>
             <?php else: ?>
-                <?= Studip\Button::create($button_label, 'continue', ['style' => 'visibility: hidden;']) ?>
+                <?= Studip\Button::create($button_label ?? '', 'continue', ['style' => 'visibility: hidden;']) ?>
             <?php endif; ?>
             </div>
         </div>

lib/classes/SystemChecker.php

@@ -113,7 +113,11 @@ final class SystemChecker
         $settings = [];
         $settings_valid = true;
         foreach ($requirements['settings'] as $setting => $state) {
-            $settings[$setting] = $this->compareSetting($variables[$setting], $state, $version['present']);
+            $settings[$setting] = $this->compareSetting(
+                $variables[$setting] ?? null,
+                $state,
+                $version['present']
+            );
 
             $settings_valid = $settings_valid && $settings[$setting]['valid'];
         }