[Settings] Avoid from crash - SystemProp default null

Default system properties should not have "null" as default value.

Bug: 177843016
Change-Id: Idc2b3aaafd1094ba3fbfa859c4ad7a597e1b7a99
Test: build pass
(cherry picked from commit d2eda630e2dc42ca4efdb0a45702de8452dd78c7)
1 file changed