change NULL to nullptr am: b6d091ccf2

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2924887

Change-Id: Ie7ffde14308c32d56cd3f4c14e5adcd1d402658f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>