diff --git a/UserInQueueService.php b/UserInQueueService.php
index fd9d8c6..1df5038 100644
--- a/UserInQueueService.php
+++ b/UserInQueueService.php
@@ -221,7 +221,7 @@ private function getQueryString(
 
     private function generateRedirectUrl($queueDomain, $uriPath, $query)
     {
-        if (substr($queueDomain, -1) !== "/")
+    	if (substr($queueDomain ?? '', -1) !== "/")
             $queueDomain = $queueDomain . "/";
 
         return "https://" . $queueDomain . $uriPath . "?" . $query;
diff --git a/UserInQueueStateCookieRepository.php b/UserInQueueStateCookieRepository.php
index a8a1d61..7ef38b8 100644
--- a/UserInQueueStateCookieRepository.php
+++ b/UserInQueueStateCookieRepository.php
@@ -57,11 +57,11 @@ private function createCookieValue($eventId, $queueId, $fixedCookieValidityMinut
 
     private function getCookieNameValueMap($cookieValue) {
         $result = array();
-        $cookieNameValues = explode("&", $cookieValue);
+	$cookieNameValues = explode("&", $cookieValue ?? '');
         $length = count($cookieNameValues);
 
         for ($i = 0; $i < $length; ++$i) {
-            $arr = explode("=", $cookieNameValues[$i]);
+    	    $arr = explode("=", $cookieNameValues[$i] ?? '');
             if (count($arr) == 2) {
                 $result[$arr[0]] = $arr[1];
             }