Merge pull request #10550 from benmosher/strict-null-check-proxy

Allow undefined from ProxyHandler<T>.getOwnPropertyDescriptor

Author: mhegazy

lib/lib.es2015.proxy.d.ts

@@ -19,7 +19,7 @@ interface ProxyHandler<T> {
     setPrototypeOf? (target: T, v: any): boolean;
     isExtensible? (target: T): boolean;
     preventExtensions? (target: T): boolean;
-    getOwnPropertyDescriptor? (target: T, p: PropertyKey): PropertyDescriptor;
+    getOwnPropertyDescriptor? (target: T, p: PropertyKey): PropertyDescriptor | undefined;
     has? (target: T, p: PropertyKey): boolean;
     get? (target: T, p: PropertyKey, receiver: any): any;
     set? (target: T, p: PropertyKey, value: any, receiver: any): boolean;
@@ -35,4 +35,4 @@ interface ProxyConstructor {
     revocable<T>(target: T, handler: ProxyHandler<T>): { proxy: T; revoke: () => void; };
     new <T>(target: T, handler: ProxyHandler<T>): T
 }
-declare var Proxy: ProxyConstructor;
+declare var Proxy: ProxyConstructor;