Typo, we have to check expiresAfter with null values

Author: Nyholm

src/CachePoolTest.php

@@ -549,7 +549,7 @@ public function testExpiresAfterWithNull()
 
         $item = $this->cache->getItem('key');
         $item->set('value');
-        $item->expiresAt(null);
+        $item->expiresAfter(null);
         $this->cache->save($item);
 
         $item = $this->cache->getItem('key');