Merge "Nullability check for mount module." am: 7b90c81b7c am: 63fa646854

Original change: https://android-review.googlesource.com/c/platform/bionic/+/2539232

Change-Id: I2df8c9584fc6f59142057a85f728599dbda67e35
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>