When timestamp is not defined

src/Collector/Neo4jDataCollector.php

@@ -70,7 +70,7 @@ public function collect(Request $request, Response $response, ?\Throwable $excep
         $mergedArray = array_merge($successfulStatements, $failedStatements);
         uasort(
             $mergedArray,
-            static fn (array $a, array $b) => $a['start_time'] <=> $b['timestamp']
+            static fn (array $a, array $b) => $a['start_time'] <=> ($b['timestamp'] ?? $b['start_time'])
         );
         $this->data['statements'] = $mergedArray;
     }