From ac0438e07b390f06fe53b2375ba9ea461361b805 Mon Sep 17 00:00:00 2001
From: Mei-Hui Su <mei@Mei-Huis-MacBook-Air.local>
Date: Tue, 19 Jan 2016 22:36:19 -0800
Subject: [PATCH] Fix the optional check to include null

---
 src/drawer.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/drawer.js b/src/drawer.js
index 4190bbea..7567e354 100644
--- a/src/drawer.js
+++ b/src/drawer.js
@@ -384,7 +384,7 @@ $.Drawer.prototype = /** @lends OpenSeadragon.Drawer.prototype */{
 
         this.context.save();
         this.context.globalAlpha = opacity;
-        if (compositeOperation !== undefined) {
+        if (compositeOperation !== undefined && compositeOperation !== null) {
             this.context.globalCompositeOperation = compositeOperation;
         }
         this.context.drawImage(