IRI fields break if value has trailing slash

[dennisvang]

Problem

IRI fields with trailing slash are rendered empty in the UI and in the RDF preview, but they do end up correctly in the triple store.

How to reproduce

1. run compose/fdp/ephemeral/v1
2. visit http://localhost in the browser
3. log in as default admin
4. click "Edit"
5. click "View RDF"
6. fill out an empty IRI form field, e.g. Rights, with value http://example.com
7. observe the expected result in the RDF preview:

    dct:rights <http://example.com>;

8. now add a trailing slash, as in http://example.com/
9. observe the error in the RDF preview:

    dct:rights ex:;

10. click "Save"
11. observe that the resulting value does pass validation (there are no validation errors), but the field shows up empty in the UI:

12. click the "ttl" button to view the actual RDF
13. observe that the field value does show up properly in the final RDF obtained from the triple store:

  dcterms:rights <http://example.com/>;

14. (also note the discrepancy in prefixes: dct: in preview, dcterms: in final result)