From e8b4b7f106f6af98bd8e4204b893b1449add2e16 Mon Sep 17 00:00:00 2001
From: bakpakin <calsrose@gmail.com>
Date: Sat, 28 Mar 2015 21:03:42 +0800
Subject: [PATCH] Fix small but devestating bug for systems without Entities.

---
 jojo.lua | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/jojo.lua b/jojo.lua
index ad701eb..b0becf9 100644
--- a/jojo.lua
+++ b/jojo.lua
@@ -340,8 +340,10 @@ function World:updateSystem(system, dt)
     if update then
         local entities = self.entities
         local eids = systemEntities[system.id]
-        for eid in pairs(eids) do
-            update(entities[eid], dt)
+        if eids then
+            for eid in pairs(eids) do
+                update(entities[eid], dt)
+            end
         end
     end
 end