From 1af7d4a894ad809de6424d043600e32e7c01bda9 Mon Sep 17 00:00:00 2001
From: Guo Xiang Tan <tgx_world@hotmail.com>
Date: Tue, 19 Jun 2018 15:25:44 +0800
Subject: [PATCH] FIX: Don't try to dequeue an empty queue.

---
 lib/scheduler/defer.rb | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/scheduler/defer.rb b/lib/scheduler/defer.rb
index 7a2e8f53cb4..0c71e5e0b48 100644
--- a/lib/scheduler/defer.rb
+++ b/lib/scheduler/defer.rb
@@ -62,6 +62,7 @@ module Scheduler
 
     # using non_block to match Ruby #deq
     def do_work(non_block = false)
+      return unless @queue.size > 0
       db, job, desc = @queue.deq(non_block)
       db ||= RailsMultisite::ConnectionManagement::DEFAULT