Merge pull request #3410 from robertknight/3409-style-null-to-nonnull

Fix incorrect update of style when props.style transitions from null to non-null
(cherry picked from commit bcd70ad500)

src/browser/ui/ReactDOMComponent.js

@@ -350,6 +350,7 @@ ReactDOMComponent.Mixin = {
             styleUpdates[styleName] = '';
           }
         }
+        this._previousStyleCopy = null;
       } else if (registrationNameModules.hasOwnProperty(propKey)) {
         deleteListener(this._rootNodeID, propKey);
       } else if (

src/browser/ui/__tests__/ReactDOMComponent-test.js

@@ -152,6 +152,17 @@ describe('ReactDOMComponent', function() {
       expect(stubStyle.color).toEqual('');
     });
 
+    it("should update styles when 'style' changes from null to object", function() {
+      var container = document.createElement('div');
+      var styles = {color: 'red'};
+      React.render(<div style={styles} />, container);
+      React.render(<div />, container);
+      React.render(<div style={styles} />, container);
+
+      var stubStyle = container.firstChild.style;
+      expect(stubStyle.color).toEqual('red');
+    });
+
     it("should empty element when removing innerHTML", function() {
       var container = document.createElement('div');
       React.render(<div dangerouslySetInnerHTML={{__html: ':)'}} />, container);