Fix b/243485315: NullPointerException when getAppBatteryUsageData().

Bug: 243485315
Fix: 243485315
Test: presubmit
Change-Id: I8bb2db7976f6c8817e9ab45fe3a40456afcd8128
diff --git a/src/com/android/settings/fuelgauge/batteryusage/BatteryChartPreferenceController.java b/src/com/android/settings/fuelgauge/batteryusage/BatteryChartPreferenceController.java
index 45ae8c5..f3fec8e 100644
--- a/src/com/android/settings/fuelgauge/batteryusage/BatteryChartPreferenceController.java
+++ b/src/com/android/settings/fuelgauge/batteryusage/BatteryChartPreferenceController.java
@@ -697,12 +697,13 @@
 
         final Map<Integer, Map<Integer, BatteryDiffData>> batteryUsageData =
                 DataProcessor.getBatteryUsageData(context, batteryHistoryMap);
-        return batteryUsageData == null
-                ? null
-                : batteryUsageData
-                        .get(BatteryChartViewModel.SELECTED_INDEX_ALL)
-                        .get(BatteryChartViewModel.SELECTED_INDEX_ALL)
-                        .getAppDiffEntryList();
+        if (batteryUsageData == null) {
+            return null;
+        }
+        BatteryDiffData allBatteryDiffData = batteryUsageData.get(
+                BatteryChartViewModel.SELECTED_INDEX_ALL).get(
+                BatteryChartViewModel.SELECTED_INDEX_ALL);
+        return allBatteryDiffData == null ? null : allBatteryDiffData.getAppDiffEntryList();
     }
 
     /** Used for {@link AppBatteryPreferenceController}. */