Merge "Nullability check for mman module." am: b72900c5c9

Original change: https://android-review.googlesource.com/c/platform/bionic/+/2580311

Change-Id: I9de3a0e0689e51725ca755066c7ff2faa09edd54
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>