diff --git a/android/src/main/java/com/ninty/system/setting/SystemSetting.java b/android/src/main/java/com/ninty/system/setting/SystemSetting.java
index dedd524..844fdab 100644
--- a/android/src/main/java/com/ninty/system/setting/SystemSetting.java
+++ b/android/src/main/java/com/ninty/system/setting/SystemSetting.java
@@ -246,6 +246,7 @@ public void run() {
     public void getAppBrightness(Promise promise) {
         final Activity curActivity = getCurrentActivity();
         if (curActivity == null) {
+            promise.reject("-1", "cannot get app brightness: current activity is null");
             return;
         }
         try {