Adding hippotaxonomy:category to document type throws javax.jcr.nodetype.ConstraintViolationException:

Steps to reproduce
1) Create new project from archetype and add the Taxonomy feature.
2) In the CMS add New document type
3) click Compound Field / Category
Expected: Category added and saved

Actual:
Exception logged. When clicking Done dialog 'An error occurred, please retry.'

Stacktrace:

ERROR http-nio-8080-exec-3 [FieldPluginEditorPlugin$PropertyEditor.getClusterParameters:158] failed to add child node to plugin config
[INFO] [talledLocalContainer] javax.jcr.nodetype.ConstraintViolationException: /hippo:namespaces/myhippoproject/ajc/hipposysedit:prototypes/hipposysedit:prototype/myhippoproject:hippotaxonomy_category: mandatory property

key does not exist
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.ItemSaveOperation.validateTransientItems(ItemSaveOperation.java:537)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.ItemSaveOperation.perform(ItemSaveOperation.java:216)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:216)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.ItemImpl.perform(ItemImpl.java:91)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:329)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.session.SessionSaveOperation.perform(SessionSaveOperation.java:65)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.session.SessionState.perform(SessionState.java:216)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.SessionImpl.perform(SessionImpl.java:365)
[INFO] [talledLocalContainer] at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:816)
[INFO] [talledLocalContainer] at org.hippoecm.repository.decorating.SessionDecorator.save(SessionDecorator.java:192)
[INFO] [talledLocalContainer] at org.hippoecm.repository.impl.SessionDecorator.save(SessionDecorator.java:180)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.editor.plugins.field.FieldPluginEditorPlugin$PropertyEditor.getClusterParameters(FieldPluginEditorPlugin.java:156)
[INFO] [talledLocalContainer] at org.hippoecm.frontend.editor.plugins.field.FieldPluginEditorPlugin$PropertyEditor.onBeforeRender(FieldPluginEditorPlugin.java:131)
[INFO] [talledLocalContainer] at org.apache.wicket.Component.internalBeforeRender(Component.java:949)

Also a warning:
WARN http-nio-8080-exec-3 [AbstractTextComponent.getModelType:170] Couldn't resolve model type of Model:classname=[org.apache.wicket.model.PropertyModel]:nestedModel=[Model:classname=[org.apache.wicket.model.Model]:object=[JcrPluginConfig:/hippo:namespaces/myhippoproject/ajc/editor:templates/_default_/hippotaxonomy_category]]:expression=[caption] for [TextField [Component id = widget]], please set the type yourself.