NPE fix: log sensor timestamp only when sensor is not empty

I tried writing test for it but the problem is making `Trace.isTagEnabled` return true.
And anyway this is easy fix so hopefully test is just nice to have.

Test: manual
Fixes: 401728609
Flag: EXEMPT trivial fix
Change-Id: Ib4f8b962d05aff9eaaf23fc865bf53e30a4231ba

1 files changed, 2 insertions, 1 deletions

diff --git a/services/foldables/devicestateprovider/src/com/android/server/policy/FoldableDeviceStateProvider.java b/services/foldables/devicestateprovider/src/com/android/server/policy/FoldableDeviceStateProvider.java
index de78271acddc..69e856de401a 100644
--- a/services/foldables/devicestateprovider/src/com/android/server/policy/FoldableDeviceStateProvider.java
+++ b/services/foldables/devicestateprovider/src/com/android/server/policy/FoldableDeviceStateProvider.java
@@ -325,7 +325,8 @@ public final class FoldableDeviceStateProvider implements DeviceStateProvider,
             }
 
             if (newState != INVALID_DEVICE_STATE_IDENTIFIER && newState != mLastReportedState) {
-                if (Trace.isTagEnabled(TRACE_TAG_SYSTEM_SERVER)) {
+                if (mLastHingeAngleSensorEvent != null
+                        && Trace.isTagEnabled(TRACE_TAG_SYSTEM_SERVER)) {
                     Trace.instant(TRACE_TAG_SYSTEM_SERVER,
                             "[Device state changed] Last hinge sensor event timestamp: "
                                     + mLastHingeAngleSensorEvent.timestamp);