When adding xinha field to a type - error msg displayed without workaround

when adding hippostd:html the following error msg is displayed (dutch):

Een verplicht veld is niet ingevuld. Geef het veplichte veld, aangegeven met een *, een waarde.

There is no workaround.

The same holds for hippo:resource - although in this case there is a workaround by uploading a dummy image

If you add a hippo:resource to a compound and upload a dummy image then adding this compound to a document type gives also the same error message, without a workaround.

Exception seen during update-all-content (I guess):

Caused by: java.lang.NullPointerException
at org.hippoecm.frontend.editor.plugins.linkpicker.MirrorTemplatePlugin$
1.getObject(MirrorTemplatePlugin.java:66)
at org.apache.wicket.Component.getModelObject(Component.java:1558)
at org.apache.wicket.Component.getModelObjectAsString(Component.java:158
0)
at org.apache.wicket.markup.html.basic.Label.onComponentTagBody(Label.ja
va:111)
at org.apache.wicket.Component.renderComponent(Component.java:2480)
... 126 more