Handle nullable sysprop for tryParseBoolean am: c573b71d2a

Original change: https://android-review.googlesource.com/c/platform/system/tools/sysprop/+/2261078

Change-Id: I411eebdc2c83d9bafe8266bcfce1fbe0c143a859
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>