Fix kotlin nullable errors in PackageInstallerSessions

Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.

Bug: 294110802
Test: builds
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9de59d6e94521e39bb5c30ec3e4d576e06a93df7)
Merged-In: Ia6e9d146eb5fd31b1c27664080c50398a147b1e4

Change-Id: Ia6e9d146eb5fd31b1c27664080c50398a147b1e4
diff --git a/core/tests/PackageInstallerSessions/src/android/content/pm/PackageSessionTests.kt b/core/tests/PackageInstallerSessions/src/android/content/pm/PackageSessionTests.kt
index 9acb99a8..b794352 100644
--- a/core/tests/PackageInstallerSessions/src/android/content/pm/PackageSessionTests.kt
+++ b/core/tests/PackageInstallerSessions/src/android/content/pm/PackageSessionTests.kt
@@ -445,7 +445,9 @@
                     Manifest.permission.UPDATE_PACKAGES_WITHOUT_USER_ACTION)
         }
         handlerThread = HandlerThread("PackageSessionTests")
-        handlerThread?.start()
-        handler = Handler(handlerThread?.looper)
+        handlerThread?.let {
+            it.start()
+            handler = Handler(it.looper)
+        }
     }
 }