From 4e20882ac01df80fff4b9ab97fca968bc0bcc3bf Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Thu, 27 Oct 2016 08:43:22 -0700
Subject: [PATCH] Fix: test for presence, not absence

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

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
index 6273d2b3117..8c0da2562e9 100644
--- a/src/compiler/program.ts
+++ b/src/compiler/program.ts
@@ -333,7 +333,7 @@ namespace ts {
         if (host.resolveModuleNames) {
             resolveModuleNamesWorker = (moduleNames, containingFile) => host.resolveModuleNames(moduleNames, containingFile).map(resolved => {
                 // An older host may have omitted extension, in which case we should infer it from the file extension of resolvedFileName.
-                if (!resolved || resolved.extension === undefined) {
+                if (!resolved || resolved.extension !== undefined) {
                     return resolved;
                 }
                 resolved = clone(resolved);