From 3a7e29674bc9223d0173ad49737f98ebab28d110 Mon Sep 17 00:00:00 2001
From: Jermolene <jeremy@jermolene.com>
Date: Thu, 2 Jul 2015 17:33:51 +0100
Subject: [PATCH] Fix problem with checkbox widget and missing tiddlers
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The newly added invertTag code was crashing if the tiddler doesn’t
exist.
---
 core/modules/widgets/checkbox.js | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/core/modules/widgets/checkbox.js b/core/modules/widgets/checkbox.js
index cd6ff2045..c349fd4bb 100644
--- a/core/modules/widgets/checkbox.js
+++ b/core/modules/widgets/checkbox.js
@@ -95,11 +95,12 @@ CheckboxWidget.prototype.handleChangeEvent = function(event) {
 		fallbackFields = {text: ""},
 		newFields = {title: this.checkboxTitle},
 		hasChanged = false,
-		tagCheck = false;
+		tagCheck = false,
+		hasTag = tiddler && tiddler.hasTag(this.checkboxTag);
 	if(this.checkboxTag && this.checkboxInvertTag === "yes") {
-		tagCheck = tiddler.hasTag(this.checkboxTag) === checked;
+		tagCheck = hasTag === checked;
 	} else {
-		tagCheck = tiddler.hasTag(this.checkboxTag) !== checked;
+		tagCheck = hasTag !== checked;
 	}
 	// Set the tag if specified
 	if(this.checkboxTag && (!tiddler || tagCheck)) {