fix getDuplicateJobs fails due to $job->getId() returning an empy string

fix issue https://www.drupal.org/project/advancedqueue/issues/3495163

src/Plugin/AdvancedQueue/Backend/Database.php

@@ -213,7 +213,7 @@ class Database extends BackendBase implements SupportsDeletingJobsInterface, Sup
       ->condition('fingerprint', $fingerprint)
       ->condition('state', [Job::STATE_QUEUED, Job::STATE_PROCESSING], 'IN');
 
-    if ($job->getId() !== NULL) {
+    if (!empty($job->getId())) {
       $query->condition('job_id', $job->getId(), '<>');
     }
     $result = $query->execute();