Promises: make null a legal argument for .then

test/mjsunit/es6/promises.js

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 82 matching lines @@
 (function() {
   Promise.reject(5).chain(assertUnreachable, undefined).chain(
     assertUnreachable,
     function(r) { assertAsync(r === 5, "rejected/chain-nohandler") }
   )
   assertAsyncRan()
 })();
 
 (function() {
   Promise.resolve(5).then(undefined, assertUnreachable).chain(
-    function(x) { assertAsync(x === 5, "resolved/then-nohandler") },
+    function(x) { assertAsync(x === 5, "resolved/then-nohandler-undefined") },
     assertUnreachable
   )
   assertAsyncRan()
+  Promise.resolve(6).then(null, assertUnreachable).chain(
+    function(x) { assertAsync(x === 6, "resolved/then-nohandler-null") },
+    assertUnreachable
+  )
+  assertAsyncRan()
 })();
 
 (function() {
   Promise.reject(5).then(assertUnreachable, undefined).chain(
     assertUnreachable,
-    function(r) { assertAsync(r === 5, "rejected/then-nohandler") }
+    function(r) { assertAsync(r === 5, "rejected/then-nohandler-undefined") }
+  )
+  assertAsyncRan()
+  Promise.reject(6).then(assertUnreachable, null).chain(
+    assertUnreachable,
+    function(r) { assertAsync(r === 6, "rejected/then-nohandler-null") }
   )
   assertAsyncRan()
 })();
 
 (function() {
   var p1 = Promise.resolve(5)
   var p2 = Promise.resolve(p1)
   var p3 = Promise.resolve(p2)
   p3.chain(
     function(x) { assertAsync(x === p2, "resolved/chain") },
@@ skipping 659 matching lines @@
   Promise.all([11, Promise.resolve(12), 13, MyPromise.resolve(14), 15, 16])
   assertTrue(log === "nx14cn", "subclass/all/arg")
 
   log = ""
   MyPromise.all([21, Promise.resolve(22), 23, MyPromise.resolve(24), 25, 26])
   assertTrue(log === "nx24nnx21cnnx23cncnnx25cnnx26cn", "subclass/all/self")
 })();
 
 
 assertAsyncDone()