Set tracer only when available (ongr-io#910)

Author: alexander-schranz

Service/ManagerFactory.php

@@ -103,7 +103,10 @@ public function createManager($managerName, $connection, $analysis, $managerConf
 
         $client = ClientBuilder::create();
         $client->setHosts($connection['hosts']);
-        $client->setTracer($this->tracer);
+
+        if ($this->tracer) {
+            $client->setTracer($this->tracer);
+        }
 
         if ($this->logger && $managerConfig['logger']['enabled']) {
             $client->setLogger($this->logger);