From 5edf72666d62cbdefaf4a31513c61451c5a9fc01 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Wed, 11 May 2016 09:26:03 -0700
Subject: [PATCH] Revert to declared type when '!' postfix operator would
 produce 'nothing'

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

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2bc0893899..b0bdca3c41 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -7621,6 +7621,9 @@ namespace ts {
             const visitedFlowStart = visitedFlowCount;
             const result = getTypeAtFlowNode(reference.flowNode);
             visitedFlowCount = visitedFlowStart;
+            if (reference.parent.kind === SyntaxKind.NonNullExpression && getTypeWithFacts(result, TypeFacts.NEUndefinedOrNull) === nothingType) {
+                return declaredType;
+            }
             return result;
 
             function getTypeAtFlowNode(flow: FlowNode): Type {