diff --git a/src/Server/Transport/Sse/Store/CachePoolStore.php b/src/Server/Transport/Sse/Store/CachePoolStore.php
index 68a476fb..02e3001e 100644
--- a/src/Server/Transport/Sse/Store/CachePoolStore.php
+++ b/src/Server/Transport/Sse/Store/CachePoolStore.php
@@ -45,6 +45,11 @@ public function pop(Uuid $id): ?string
         }
 
         $messages = $item->get();
+
+        if ([] === $messages) {
+            return null;
+        }
+
         $message = array_shift($messages);
 
         $item->set($messages);