Avoid NPE when getting last shutdown reason.

This can be null if there is a file but it's totally empty, and the
switch statement will throw an NPE when switching on a null string
(thanks Java!)

Bug: 38195795
Test: none
Change-Id: I86901e001b088a4a9b14f15c82b763e12d11875f

1 files changed, 3 insertions, 0 deletions

diff --git a/services/core/java/com/android/server/power/PowerManagerService.java b/services/core/java/com/android/server/power/PowerManagerService.java
index 423bc0cc7884..a8d19e94dea5 100644
--- a/services/core/java/com/android/server/power/PowerManagerService.java
+++ b/services/core/java/com/android/server/power/PowerManagerService.java
@@ -4607,6 +4607,9 @@ public final class PowerManagerService extends SystemService
         } catch (IOException e) {
             Slog.e(TAG, "Failed to read last_reboot_reason file", e);
         }
+        if (line == null) {
+            return PowerManager.SHUTDOWN_REASON_UNKNOWN;
+        }
         switch (line) {
             case REASON_SHUTDOWN:
                 return PowerManager.SHUTDOWN_REASON_SHUTDOWN;