Explicit format selection fails in the absence of Accept headers

[der]

Formerly a curl http://myregistr/myregister?_format=xxx would return data follow the selected format include ttl, rdf and jsonld.

In current registry-core this will always return text/csv independent of _format argument.

Underlying case is that the JAX-RS routing is no longer calling the defaultRead endpoint (which has not explicit @Produces) and instead picking one of the typed endpoints. Not clear why this is happening now, the JAX-RS version and implementation has not changed for many years.