Check whether stack is non-empty before popping (exception and other listeners can stop event propagation)

Author: allflame

src/Bridge/RequestSpanListener.php

@@ -57,6 +57,11 @@ public function getOperationName(Request $request)
 
     public function onResponse(FilterResponseEvent $event)
     {
+        if ($this->spans->isEmpty()) {
+
+            return $this;
+        }
+
         $this->tracer->finish(
             $this->spans->pop()->addTag(new HttpCodeTag($event->getResponse()->getStatusCode()))
         );