Merge "Nullability check for poll module." am: cb5188d4c8

Original change: https://android-review.googlesource.com/c/platform/bionic/+/2617335

Change-Id: I9cee7e1ce60d88de5257354a6312c37a4be49fbd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>