The Contributors page created by "Add contributors" has no version in its EntryClass object

Steps to reproduce

1. Create a release note for a product and a version (e.g. XWiki / 8.3M1)
2. On the release note, click the "Add contributors" button of the Credits section
3. Fill in some contributors and save

Expected

The created Contributors page carries the product, version and type of the release note in its ReleaseNotes.Code.EntryClass object.

Actual

The version property of the ReleaseNotes.Code.EntryClass object is empty. product and type only look right because ReleaseNotes.Code.ContributorsTemplate happens to hold XWiki and Contributors as defaults, so a release note of another product gets XWiki as well.

Cause

The button passes product, version and type as request parameters. ReleaseNotes.Code.ContributorsSheet copies them on the in-memory entry object when displaying the edit form, but does not put them in the form. On save, the page is rebuilt from the template and the submitted fields only, so these values are lost.