From a0790fba7df3ee2109282a56d2635bfd3a09c35c Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Fri, 4 Mar 2016 17:39:56 -0800
Subject: [PATCH] Add only 'undefined' to optional parameter types

---
 src/compiler/checker.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 15a57ed8931..9384145164e 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2698,7 +2698,7 @@ namespace ts {
             // Use type from type annotation if one is present
             if (declaration.type) {
                 const type = getTypeFromTypeNode(declaration.type);
-                return declaration.questionToken ? getNullableType(type) : type;
+                return strictNullChecks && declaration.questionToken ? addNullableKind(type, TypeFlags.Undefined) : type;
             }
 
             if (declaration.kind === SyntaxKind.Parameter) {
@@ -2713,7 +2713,7 @@ namespace ts {
                 // Use contextual parameter type if one is available
                 const type = getContextuallyTypedParameterType(<ParameterDeclaration>declaration);
                 if (type) {
-                    return declaration.questionToken ? getNullableType(type) : type;
+                    return strictNullChecks && declaration.questionToken ? addNullableKind(type, TypeFlags.Undefined) : type;
                 }
             }