fixed the issue

src/CronJobManager.php

@@ -77,7 +77,10 @@ class CronJobManager implements CronJobManagerInterface {
       'status' => TRUE,
     ]);
 
-    return $jobs ? reset($jobs) : NULL;
+    if (is_array($jobs) && !empty($jobs)) {
+      return reset($jobs);
+    }
+    return NULL;
   }
 
   /**