[7.8] Add root folder dialog throws NPE.

Encountered this problem while testing REPO-1293, using repository 2.24.17-SNAPSHOT (as of the creation date of this issue).

Actions:

1) create and start archetype project
2) login as admin, navigate to documents perpective
3) Click "Add root folder", dialog opens
4) Without/before filling in a name/url, switch the type selection to folder

Expected: I get to see the language selection widget.
Actual: I don't get to see that widget, but I see an NPE log:

[INFO] java.lang.NullPointerException
[INFO] at org.hippoecm.repository.api.StringCodecFactory$UriEncoding.encode(StringCodecFactory.java:135)
[INFO] at org.hippoecm.frontend.plugins.standardworkflow.components.NameUriField.encodeUri(NameUriField.java:165)
[INFO] at org.hippoecm.frontend.plugins.standardworkflow.FolderShortcutPlugin$Dialog$4.onUpdate(FolderShortcutPlugin.java:359)
[INFO] at org.apache.wicket.ajax.form.AjaxFormComponentUpdatingBehavior.onEvent(AjaxFormComponentUpdatingBehavior.java:158)
[INFO] at org.apache.wicket.ajax.AjaxEventBehavior.respond(AjaxEventBehavior.java:177)
[INFO] at org.apache.wicket.ajax.AbstractDefaultAjaxBehavior.onRequest(AbstractDefaultAjaxBehavior.java:312)
[INFO] at org.apache.wicket.request.target.component.listener.BehaviorRequestTarget.processEvents(BehaviorRequestTarget.java:157)
[...]