Unbreaking falsy check on style values

Style values can be the number zero which is an actual value. So we check for
null instead. The empty string case falls through.

src/core/ReactNativeComponent.js

@@ -247,7 +247,8 @@ ReactNativeComponent.Mixin = {
         if (lastProp) {
           // Unset styles on `lastProp` but not on `nextProp`.
           for (styleName in lastProp) {
-            if (lastProp.hasOwnProperty(styleName) && !nextProp[styleName]) {
+            if (lastProp.hasOwnProperty(styleName) &&
+                !nextProp.hasOwnProperty(styleName)) {
               styleUpdates = styleUpdates || {};
               styleUpdates[styleName] = '';
             }

src/core/__tests__/ReactNativeComponent-test.js

@@ -70,7 +70,7 @@ describe('ReactNativeComponent', function() {
     });
 
     it("should update styles when mutating style object", function() {
-      var styles = { display: 'none', fontFamily: 'Arial' };
+      var styles = { display: 'none', fontFamily: 'Arial', opacity: 0 };
       var stub = ReactTestUtils.renderIntoDocument(<div style={styles} />);
 
       var stubStyle = stub.getDOMNode().style;
@@ -82,12 +82,21 @@ describe('ReactNativeComponent', function() {
       stub.receiveProps({ style: styles }, transaction);
       expect(stubStyle.display).toEqual('block');
       expect(stubStyle.fontFamily).toEqual('Arial');
+      expect(stubStyle.opacity).toEqual('0');
 
       styles.fontFamily = 'Helvetica';
 
       stub.receiveProps({ style: styles }, transaction);
       expect(stubStyle.display).toEqual('block');
       expect(stubStyle.fontFamily).toEqual('Helvetica');
+      expect(stubStyle.opacity).toEqual('0');
+
+      styles.opacity = 0.5;
+
+      stub.receiveProps({ style: styles }, transaction);
+      expect(stubStyle.display).toEqual('block');
+      expect(stubStyle.fontFamily).toEqual('Helvetica');
+      expect(stubStyle.opacity).toEqual('0.5');
     });
 
     it("should update styles if initially null", function() {

src/dom/CSSPropertyOperations.js

@@ -74,8 +74,10 @@ var CSSPropertyOperations = {
       if (!styles.hasOwnProperty(styleName)) {
         continue;
       }
-      var styleValue = styles[styleName];
-      if (!styleValue) {
+      var styleValue = dangerousStyleValue(styleName, styles[styleName]);
+      if (styleValue) {
+        style[styleName] = styleValue;
+      } else {
         var expansion = CSSProperty.shorthandPropertyExpansions[styleName];
         if (expansion) {
           // Shorthand property that IE8 won't like unsetting, so unset each
@@ -86,8 +88,6 @@ var CSSPropertyOperations = {
         } else {
           style[styleName] = '';
         }
-      } else {
-        style[styleName] = dangerousStyleValue(styleName, styleValue);
       }
     }
   }