[android] fix crash if breadcrumb refs don't exist

Libraries/CustomComponents/Navigator/NavigatorBreadcrumbNavigationBar.js

@@ -119,16 +119,16 @@ var NavigatorBreadcrumbNavigationBar = React.createClass({
     }
 
     if (interpolate.Crumb(CRUMB_PROPS[index].style, amount)) {
-      this.refs['crumb_' + index].setNativeProps(CRUMB_PROPS[index]);
+      this._setPropsIfExists('crumb_' + index, CRUMB_PROPS[index]);
     }
     if (interpolate.Icon(ICON_PROPS[index].style, amount)) {
-      this.refs['icon_' + index].setNativeProps(ICON_PROPS[index]);
+      this._setPropsIfExists('icon_' + index, ICON_PROPS[index]);
     }
     if (interpolate.Separator(SEPARATOR_PROPS[index].style, amount)) {
-      this.refs['separator_' + index].setNativeProps(SEPARATOR_PROPS[index]);
+      this._setPropsIfExists('separator_' + index, SEPARATOR_PROPS[index]);
     }
     if (interpolate.Title(TITLE_PROPS[index].style, amount)) {
-      this.refs['title_' + index].setNativeProps(TITLE_PROPS[index]);
+      this._setPropsIfExists('title_' + index, TITLE_PROPS[index]);
     }
     var right = this.refs['right_' + index];
     if (right &&
@@ -165,13 +165,10 @@ var NavigatorBreadcrumbNavigationBar = React.createClass({
       renderToHardwareTextureAndroid: renderToHardwareTexture,
     };
 
-    this.refs['icon_' + index].setNativeProps(props);
+    this._setPropsIfExists('icon_' + index, props);
-    this.refs['separator_' + index].setNativeProps(props);
+    this._setPropsIfExists('separator_' + index, props);
-    this.refs['title_' + index].setNativeProps(props);
+    this._setPropsIfExists('title_' + index, props);
-    var right = this.refs['right_' + index];
+    this._setPropsIfExists('right_' + index, props);
-    if (right) {
-      right.setNativeProps(props);
-    }
   },
 
   componentWillMount: function() {
@@ -260,6 +257,11 @@ var NavigatorBreadcrumbNavigationBar = React.createClass({
     this._descriptors.right = this._descriptors.right.set(route, rightButtonDescriptor);
     return rightButtonDescriptor;
   },
+
+  _setPropsIfExists: function(ref, props) {
+    var ref = this.refs[ref];
+    ref && ref.setNativeProps(props);
+  },
 });
 
 var styles = StyleSheet.create({