Fix NPE am: a3e2e68fd0

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17591433

Change-Id: Ia465094b84a788e0a3b824a4cdf787899149bb26
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

services/core/java/com/android/server/pm/PackageInstallerService.java

@@ -390,7 +390,10 @@ public class PackageInstallerService extends IPackageInstaller.Stub implements
                     // Their staging dirs will be removed too
                     PackageInstallerSession root = !session.hasParentSessionId()
                             ? session : mSessions.get(session.getParentSessionId());
-                    if (!root.isDestroyed()) {
+                    if (root == null) {
+                        Slog.e(TAG, "freeStageDirs: found an orphaned session: "
+                                + session.sessionId + " parent=" + session.getParentSessionId());
+                    } else if (!root.isDestroyed()) {
                         root.abandon();
                     }
                 } else {