fix possible NPE in StatusBarModule

Summary:
This diff fixes a NPE happening in StatusBarModule when the style passed by parameter is null.
Even if JS shoulnd't send a null value, this method should not crash with an NPE. I'm not changing behavior, only avoiding NPE when status is null

Reviewed By: RSNara

Differential Revision: D13287057

fbshipit-source-id: cc5ac4e97083d63f2bf65c03bac0dc9bce976423

Author: mdvacca

ReactAndroid/src/main/java/com/facebook/react/modules/statusbar/StatusBarModule.java

@@ -166,7 +166,7 @@ public void run() {
   }
 
   @ReactMethod
-  public void setStyle(final String style) {
+  public void setStyle(@Nullable final String style) {
     final Activity activity = getCurrentActivity();
     if (activity == null) {
       FLog.w(ReactConstants.TAG, "StatusBarModule: Ignored status bar change, current activity is null.");
@@ -181,7 +181,7 @@ public void setStyle(final String style) {
           public void run() {
             View decorView = activity.getWindow().getDecorView();
             decorView.setSystemUiVisibility(
-              style.equals("dark-content") ? View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR : 0);
+              "dark-content".equals(style) ? View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR : 0);
           }
         }
       );