fix instance null when involve async destruction

src/renderers/shared/reconciler/ReactOwner.js

@@ -95,9 +95,10 @@ var ReactOwner = {
       '`render` method, or you have multiple copies of React loaded ' +
       '(details: https://fb.me/react-refs-must-have-owner).'
     );
-    // Check that `component` is still the current ref because we do not want to
-    // detach the ref if another component stole it.
-    if (owner.getPublicInstance().refs[ref] === component.getPublicInstance()) {
+    var ownerPublicInstance = owner.getPublicInstance();
+    // Check that `component`'s owner is still alive and that `component` is still the current ref
+    // because we do not want to detach the ref if another component stole it.
+    if (ownerPublicInstance && ownerPublicInstance.refs[ref] === component.getPublicInstance()) {
       owner.detachRef(ref);
     }
   },

src/renderers/shared/reconciler/__tests__/refs-destruction-test.js

@@ -59,4 +59,46 @@ describe('refs-destruction', function() {
     ReactDOM.render(<TestComponent destroy={true} />, container);
     expect(Object.keys(testInstance.refs || {}).length).toEqual(0);
   });
+
+  it('should not error when destroying child with ref asynchronously', function() {
+    var Modal = React.createClass({
+      componentDidMount: function() {
+        this.div = document.createElement('div');
+        document.body.appendChild(this.div);
+        this.componentDidUpdate();
+      },
+      componentDidUpdate: function() {
+        ReactDOM.render(<div>{this.props.children}</div>, this.div);
+      },
+      componentWillUnmount: function() {
+        var self = this;
+        // some async animation
+        setTimeout(function() {
+          expect(function() {
+            ReactDOM.unmountComponentAtNode(self.div);
+          }).not.toThrow();
+          document.body.removeChild(self.div);
+        }, 0);
+      },
+      render() {
+        return null;
+      },
+    });
+    var AppModal = React.createClass({
+      render: function() {
+        return (<Modal>
+          <a ref="ref"/>
+        </Modal>);
+      },
+    });
+    var App = React.createClass({
+      render: function() {
+        return this.props.hidden ? null : <AppModal onClose={this.close}/>;
+      },
+    });
+    var container = document.createElement('div');
+    ReactDOM.render(<App />, container);
+    ReactDOM.render(<App hidden={true}/>, container);
+    jest.runAllTimers();
+  });
 });