From 41401c7caeb73d45c08ea8fa2f18d90e6a401458 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 15 Feb 2016 17:02:43 -0800
Subject: [PATCH] Make types of optional parameters and properties nullable

---
 src/compiler/checker.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 1464d719478..c7e74d86f90 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -2677,7 +2677,8 @@ namespace ts {
 
             // Use type from type annotation if one is present
             if (declaration.type) {
-                return getTypeFromTypeNode(declaration.type);
+                const type = getTypeFromTypeNode(declaration.type);
+                return declaration.questionToken ? getNullableType(type) : type;
             }
 
             if (declaration.kind === SyntaxKind.Parameter) {
@@ -2692,7 +2693,7 @@ namespace ts {
                 // Use contextual parameter type if one is available
                 const type = getContextuallyTypedParameterType(<ParameterDeclaration>declaration);
                 if (type) {
-                    return type;
+                    return declaration.questionToken ? getNullableType(type) : type;
                 }
             }