diff --git a/Cache/Navitia.php b/Cache/Navitia.php
index 1a38f34..98a80cf 100644
--- a/Cache/Navitia.php
+++ b/Cache/Navitia.php
@@ -89,6 +89,7 @@ private function checkPublicationDate(): void
         if ($cacheItem->isHit()) {
             $publicationDateInCache = $cacheItem->get();
         }
+
         $currentPublicationDate = $this->getPublicationDate();
 
         if ($currentPublicationDate !== null && $currentPublicationDate !== $publicationDateInCache) {
@@ -127,7 +128,7 @@ public function setCacheItem(string $cacheKey, $data): void
         $this->cache->save($cacheItem);
     }
 
-    private function getPublicationDate(): string
+    private function getPublicationDate(): ?string
     {
         try {
             $url = $this->urlApi.'coverage/'.$this->coverage.'/'.self::PUBLICATION_DATE_API;