Response for search when null query is not supported?

[azaroth42]

It is legal to have no parameters for the search service.

For example, just

http://example.org/service/manifest/search?

The meaning is give me all of the matching annotations, no filtering. However this might not be supported. The "unsupported" mechanism is to list params that are ignored in ignored ... but here it's the opposite... the params are missing and needed, rather than present and ignored.

There's no guidance as to what to do in this case.