diff --git a/Classes/Dmailer.php b/Classes/Dmailer.php
index 9c1e83be1..1b532e14a 100644
--- a/Classes/Dmailer.php
+++ b/Classes/Dmailer.php
@@ -404,7 +404,7 @@ public function sendAdvanced(array $recipientRow, string $tableNameChar): int
             // Plain
             $this->theParts['plain']['content'] = '';
             if ($this->flagPlain) {
-                $tempContentPlain = $this->getBoundaryParts($this->dmailer['boundaryParts_plain'], $recipientRow['sys_dmail_categories_list']);
+                $tempContentPlain = $this->getBoundaryParts($this->dmailer['boundaryParts_plain'], $recipientRow['sys_dmail_categories_list'] ?? '');
                 if ($this->mailHasContent) {
                     $tempContentPlain = $this->replaceMailMarkers($tempContentPlain, $recipientRow, $additionalMarkers);
                     if (trim($this->dmailer['sys_dmail_rec']['use_rdct']) || trim($this->dmailer['sys_dmail_rec']['long_link_mode'])) {
@@ -844,7 +844,7 @@ protected function setContent(MailMessage $mailer): void
             $this->extractMediaLinks();
             foreach ($this->theParts['html']['media'] as $media) {
                 // TODO: why are there table related tags here?
-                if (in_array($media['tag'], ['img', 'table', 'tr', 'td'], true) && !$media['use_jumpurl'] && !$media['do_not_embed']) {
+                if (isset($media['tag']) && in_array($media['tag'], ['img', 'table', 'tr', 'td'], true) && !$media['use_jumpurl'] && !$media['do_not_embed']) {
                     if (ini_get('allow_url_fopen')) {
                         $context = GeneralUtility::makeInstance(FetchUtility::class)->getStreamContext();
                         if (($fp = fopen($media['absRef'], 'r', false, $context)) !== false) {
diff --git a/Classes/Module/StatisticsController.php b/Classes/Module/StatisticsController.php
index 75c23fc6a..85edcc5e7 100644
--- a/Classes/Module/StatisticsController.php
+++ b/Classes/Module/StatisticsController.php
@@ -1574,7 +1574,7 @@ public function getUrlStr(array $urlParts): string
                 $urlstr .= ($urlParts['fragment'] ?? '') ? '#' . $urlParts['fragment'] : '';
             }
         } else {
-            $urlstr =  ((isset($urlParts['host']) && $urlParts['host']) ? $urlParts['scheme'] . '://' . $urlParts['host'] : $baseUrl) . $urlParts['path'];
+            $urlstr =  ((isset($urlParts['host']) && $urlParts['host']) ? $urlParts['scheme'] . '://' . $urlParts['host'] : $baseUrl) . ($urlParts['path'] ?? '');
             $urlstr .= ($urlParts['query'] ?? '')    ? '?' . $urlParts['query']    : '';
             $urlstr .= ($urlParts['fragment'] ?? '') ? '#' . $urlParts['fragment'] : '';
         }
@@ -1653,11 +1653,11 @@ public function getLinkLabel(
 
         }
 
-        if ($this->implodedParams['showContentTitle'] == 1) {
+        if (isset($this->implodedParams['showContentTitle']) && $this->implodedParams['showContentTitle'] == 1) {
             $label = $contentTitle;
         }
 
-        if ($this->implodedParams['prependContentTitle'] == 1) {
+        if (isset($this->implodedParams['prependContentTitle']) && $this->implodedParams['prependContentTitle'] == 1) {
             $label =  $contentTitle . ' (' . $linkedWord . ')';
         }
 
diff --git a/Classes/SelectCategories.php b/Classes/SelectCategories.php
index c24af3f3c..5b298bea4 100644
--- a/Classes/SelectCategories.php
+++ b/Classes/SelectCategories.php
@@ -17,6 +17,7 @@
 
 use DirectMailTeam\DirectMail\Repository\TempRepository;
 use TYPO3\CMS\Core\Localization\LanguageService;
+use TYPO3\CMS\Core\Site\Entity\Site;
 use TYPO3\CMS\Core\Utility\GeneralUtility;
 
 /**
@@ -39,7 +40,7 @@ public function getLocalizedCategories(array &$params): void
         $lang = $this->getLang();
 
         $site = $params['site'];
-        $languages = $site->getAllLanguages();
+        $languages = ($site instanceof Site) ? $site->getAllLanguages() : [];
         foreach($languages as $language) {
             if($language->getLocale()->getLanguageCode() == $lang) {
                 $sysLanguageUid = $language->getLanguageId();