Add null check to avoid NullPointerException.

Test: make RunSettingsRoboTests
Bug: 264198981
Fix: 264198981
Change-Id: Ida2ff6beed5c0dba6329023b72e55daf1bf573f1

src/com/android/settings/fuelgauge/batteryusage/DataProcessor.java

@@ -1448,6 +1448,9 @@ public final class DataProcessor {
 
         // Calculates all packages diff usage data in a specific time slot.
         for (String key : allBatteryHistEntryKeys) {
+            if (key == null) {
+                continue;
+            }
             final BatteryHistEntry currentEntry =
                     currentBatteryHistMap.getOrDefault(key, EMPTY_BATTERY_HIST_ENTRY);
             final BatteryHistEntry nextEntry =