[PS] Return earlier if the input is null for `matches`.

In test environment, we get null string from resource, so just bypass this part.

Bug: 329442658
Test: manual
Flag: aconfig com.google.android.apps.nexuslauncher.enable_inject_private_space_tile trunkfood
Change-Id: If20586bcd882d6a705e8a670bc20a5cf5aa79ac2