From ffc4e688fa83cb44bff7e5deacc4063f8ea1e2fa Mon Sep 17 00:00:00 2001
From: Christian Kohler <kohler.christian@gmail.com>
Date: Fri, 10 May 2019 02:14:23 +0200
Subject: [PATCH] fix(Subscription): Return Empty when teardown === null
 (#4575)

* fix(Subscription): Return Empty when teardown === null

`typeof teardown` returns object when null. It breaks later when rxjs tries to access the closed property.

The commit fixes that by first checking for null/undefined.

* fix(Subscription): tslint errors
---
 src/internal/Subscription.ts | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/internal/Subscription.ts b/src/internal/Subscription.ts
index 0f1906a27e..1a07ffa508 100644
--- a/src/internal/Subscription.ts
+++ b/src/internal/Subscription.ts
@@ -130,6 +130,11 @@ export class Subscription implements SubscriptionLike {
    */
   add(teardown: TeardownLogic): Subscription {
     let subscription = (<Subscription>teardown);
+
+    if (!(<any>teardown)) {
+      return Subscription.EMPTY;
+    }
+
     switch (typeof teardown) {
       case 'function':
         subscription = new Subscription(<(() => void)>teardown);
@@ -147,9 +152,6 @@ export class Subscription implements SubscriptionLike {
         }
         break;
       default: {
-        if (!(<any>teardown)) {
-          return Subscription.EMPTY;
-        }
         throw new Error('unrecognized teardown ' + teardown + ' added to Subscription.');
       }
     }