Mark GrantPermissionsViewModel callback as nullable am: dfd3b760dd

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Permission/+/2933630

Change-Id: I099e91af6d2baefd937ad1bf82a466c56f51ae78
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>