Handle nullable sysprop for tryParseBoolean am: c573b71d2a am: 89d47269e3

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

Change-Id: I72830e70871009fe70b22c7e194e193a57320ad4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>