placeholder property
What the BLANK choice means, in the panel's own words — not decoration.
A TrashedFilter publishes "Without trashed" here, and its blank
branch really is withoutTrashed() (vendor TrashedFilter.php:27-31),
so a client that renders a generic "Any" over it tells the user the
filter was removed when it was not. Null when the node declares none,
which is the ordinary case — then the blank row genuinely is "any".
Implementation
final String? placeholder;