From 95b5a691d4b62eb3f4e59e0b72c856ad7fa2ccb8 Mon Sep 17 00:00:00 2001
From: Andrew Casey <andrew.casey@microsoft.com>
Date: Thu, 25 May 2017 14:00:11 -0700
Subject: [PATCH] Guess 1: null check is missing; Guess 2: ternary does the
 appropriate check

---
 src/server/project.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/server/project.ts b/src/server/project.ts
index 0646497acc5..524b4d816e0 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -646,7 +646,7 @@ namespace ts.server {
 
                 const added: string[] = [];
                 const removed: string[] = [];
-                const updated: string[] = arrayFrom(updatedFileNames.keys());
+                const updated: string[] = updatedFileNames ? arrayFrom(updatedFileNames.keys()) : [];
 
                 forEachKey(currentFiles, id => {
                     if (!lastReportedFileNames.has(id)) {