From 945eb7ce8139551ec009009ea9eae9e0928bd36b Mon Sep 17 00:00:00 2001
From: Jason Freeman <jfreeman@microsoft.com>
Date: Mon, 22 Sep 2014 15:09:20 -0700
Subject: [PATCH] Add undefined check for tokenPrecedingSpanStart

---
 src/services/signatureHelp.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/services/signatureHelp.ts b/src/services/signatureHelp.ts
index 03490f9b88e..103aa810de2 100644
--- a/src/services/signatureHelp.ts
+++ b/src/services/signatureHelp.ts
@@ -448,6 +448,10 @@ module ts.SignatureHelp {
 
     export function getSignatureHelpCurrentArgumentState(sourceFile: SourceFile, position: number, applicableSpanStart: number): SignatureHelpState {
         var tokenPrecedingSpanStart = ServicesSyntaxUtilities.findPrecedingToken(applicableSpanStart, sourceFile);
+        if (!tokenPrecedingSpanStart) {
+            return undefined;
+        }
+
         if (tokenPrecedingSpanStart.kind !== SyntaxKind.OpenParenToken && tokenPrecedingSpanStart.kind !== SyntaxKind.LessThanToken) {
             // The span start must have moved backward in the file (for example if the open paren was backspaced)
             return undefined;