Use empty BatteryDiffData instead of null to avoid NullPointerException

This is one action post P0 bug b/301362376.

Bug: 304067689
Bug: 303838369
Fix: 304067689
Fix: 303838369
Test: manual
Change-Id: I8bb6bfe9c3fca78ab19dfbfd2a184b0f92f4ef09
2 files changed