From 047c62c24025b9ec0086223b9248a464c6d63501 Mon Sep 17 00:00:00 2001
From: Jason Killian <jkillian@palantir.com>
Date: Fri, 15 Jan 2016 15:48:22 -0500
Subject: [PATCH] Fix issue #6478 (bug in the language services)

---
 src/services/services.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/services/services.ts b/src/services/services.ts
index 8e998760b49..062e3da1bfa 100644
--- a/src/services/services.ts
+++ b/src/services/services.ts
@@ -6028,6 +6028,10 @@ namespace ts {
              */
             function getPropertySymbolsFromBaseTypes(symbol: Symbol, propertyName: string, result: Symbol[],
                 previousIterationSymbolsCache: SymbolTable): void {
+                if (!symbol) {
+                    return;
+                }
+
                 // If the current symbol is the same as the previous-iteration symbol, we can just return the symbol that has already been visited
                 // This is particularly important for the following cases, so that we do not infinitely visit the same symbol.
                 // For example:
@@ -6043,7 +6047,7 @@ namespace ts {
                     return;
                 }
 
-                if (symbol && symbol.flags & (SymbolFlags.Class | SymbolFlags.Interface)) {
+                if (symbol.flags & (SymbolFlags.Class | SymbolFlags.Interface)) {
                     forEach(symbol.getDeclarations(), declaration => {
                         if (declaration.kind === SyntaxKind.ClassDeclaration) {
                             getPropertySymbolFromTypeReference(getClassExtendsHeritageClauseElement(<ClassDeclaration>declaration));