From acbddd26413a20afe48ca6ad681c9229933ba848 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8jberg?= <r.hackr@gmail.com>
Date: Wed, 13 Nov 2013 20:54:22 -0500
Subject: [PATCH 1/2] ReactTransitions: Don't animate undefined children

---
 .../transitions/ReactTransitionGroup.js       |  5 +++++
 .../__tests__/ReactTransitionGroup-test.js    | 21 +++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/addons/transitions/ReactTransitionGroup.js b/src/addons/transitions/ReactTransitionGroup.js
index 623838c49f4ce..9e2d4911abec4 100644
--- a/src/addons/transitions/ReactTransitionGroup.js
+++ b/src/addons/transitions/ReactTransitionGroup.js
@@ -44,6 +44,11 @@ var ReactTransitionGroupMixin = {
       'getTransitionConfig() method.'
     );
 
+    // don't animate undefined children
+    if (typeof sourceChildren === 'undefined') {
+      return;
+    }
+
     var children = {};
     var childMapping = ReactTransitionKeySet.getChildMapping(sourceChildren);
     var transitionConfig = this.getTransitionConfig();
diff --git a/src/addons/transitions/__tests__/ReactTransitionGroup-test.js b/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
index bfddd7be5ae93..8455d3fba1cab 100644
--- a/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
+++ b/src/addons/transitions/__tests__/ReactTransitionGroup-test.js
@@ -26,18 +26,18 @@ var mocks;
 // Most of the real functionality is covered in other unit tests, this just
 // makes sure we're wired up correctly.
 describe('ReactTransitionGroup', function() {
+  var container;
+
   beforeEach(function() {
     React = require('React');
     ReactTransitionGroup = require('ReactTransitionGroup');
     mocks = require('mocks');
+
+    container = document.createElement('div');
   });
 
   it('should warn after time with no transitionend', function() {
-    var container;
-    var a;
-
-    container = document.createElement('div');
-    a = React.renderComponent(
+    var a = React.renderComponent(
       <ReactTransitionGroup transitionName="yolo">
         <span key="one" id="one" />
       </ReactTransitionGroup>,
@@ -65,7 +65,6 @@ describe('ReactTransitionGroup', function() {
   });
 
   it('should keep both sets of DOM nodes around', function() {
-    var container = document.createElement('div');
     var a = React.renderComponent(
       <ReactTransitionGroup transitionName="yolo">
         <span key="one" id="one" />
@@ -83,4 +82,14 @@ describe('ReactTransitionGroup', function() {
     expect(a.getDOMNode().childNodes[0].id).toBe('two');
     expect(a.getDOMNode().childNodes[1].id).toBe('one');
   });
+
+  describe('with an undefined child', function () {
+    it('should fail silently', function () {
+      var a = React.renderComponent(
+        <ReactTransitionGroup transitionName="yolo">
+        </ReactTransitionGroup>,
+        container
+      );
+    });
+  });
 });

From 5b1e4c0324c984be96d4792b1ed13d457862a5bd Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simon=20H=C3=B8jberg?= <r.hackr@gmail.com>
Date: Wed, 13 Nov 2013 23:02:06 -0500
Subject: [PATCH 2/2] Transitions: Handle undefined input to mergeKeySet

Gracefully handle undefined input to mergeKeySet.
---
 .../transitions/ReactTransitionGroup.js       |  6 +----
 .../transitions/ReactTransitionKeySet.js      |  3 +++
 .../__tests__/ReactTransitionKeySet-test.js   | 26 +++++++++++++++++++
 3 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/src/addons/transitions/ReactTransitionGroup.js b/src/addons/transitions/ReactTransitionGroup.js
index 9e2d4911abec4..f846f208c2a09 100644
--- a/src/addons/transitions/ReactTransitionGroup.js
+++ b/src/addons/transitions/ReactTransitionGroup.js
@@ -44,13 +44,9 @@ var ReactTransitionGroupMixin = {
       'getTransitionConfig() method.'
     );
 
-    // don't animate undefined children
-    if (typeof sourceChildren === 'undefined') {
-      return;
-    }
-
     var children = {};
     var childMapping = ReactTransitionKeySet.getChildMapping(sourceChildren);
+
     var transitionConfig = this.getTransitionConfig();
     var currentKeys = ReactTransitionKeySet.mergeKeySets(
       this._transitionGroupCurrentKeys,
diff --git a/src/addons/transitions/ReactTransitionKeySet.js b/src/addons/transitions/ReactTransitionKeySet.js
index debb3073ca3f8..ebb1cdeeb930d 100644
--- a/src/addons/transitions/ReactTransitionKeySet.js
+++ b/src/addons/transitions/ReactTransitionKeySet.js
@@ -68,6 +68,9 @@ var ReactTransitionKeySet = {
    * in `next` in a reasonable order.
    */
   mergeKeySets: function(prev, next) {
+    prev = prev || {};
+    next = next || {};
+
     var keySet = {};
     var prevKeys = Object.keys(prev).concat([MERGE_KEY_SETS_TAIL_SENTINEL]);
     var nextKeys = Object.keys(next).concat([MERGE_KEY_SETS_TAIL_SENTINEL]);
diff --git a/src/addons/transitions/__tests__/ReactTransitionKeySet-test.js b/src/addons/transitions/__tests__/ReactTransitionKeySet-test.js
index 72aba5ca6f21e..993ebbc6e09d5 100644
--- a/src/addons/transitions/__tests__/ReactTransitionKeySet-test.js
+++ b/src/addons/transitions/__tests__/ReactTransitionKeySet-test.js
@@ -127,4 +127,30 @@ describe('ReactTransitionKeySet', function() {
       five: true
     });
   });
+
+  it('should support mergeKeySets with undefined input', function () {
+    var prev = {
+      one: true,
+      two: true
+    };
+
+    var next = undefined;
+
+    expect(ReactTransitionKeySet.mergeKeySets(prev, next)).toEqual({
+      one: true,
+      two: true
+    });
+
+    prev = undefined;
+
+    next = {
+      three: true,
+      four: true
+    };
+
+    expect(ReactTransitionKeySet.mergeKeySets(prev, next)).toEqual({
+      three: true,
+      four: true
+    });
+  });
 });