Taxonomies can't be created inside inspector using `createNew`

[connykaelinvisol]

Steps to reproduce:

• create a vocabulary
• create NodeType with a reference property referring to the created vocabulary
• implement createNew in the editorOptions

example

...
  properties:
    keywordAssignments:
      type: references
      ui:
        label: Keywords
        reloadIfChanged: true
        showInCreationDialog: true
        inspector:
          group: tags
          position: 10
          editorOptions:
            allowEmpty: true
            multiple: true
            nodeTypes: [ 'Sitegeist.Taxonomy:Taxonomy' ]
            startingPoint: '/taxonomies/mycreatedtaxonomy'
            createNew:
              path: /taxonomies/mycreatedtaxonomy
              type: 'Sitegeist.Taxonomy:Taxonomy'

Actual behaviour:

Get error Call to a member function getContext() on null - Check the logs for details as the createNew action searches for the next parent DocumentNode. Sitegeist.Taxonomy:Root is not Neos.Neos:Document therefore no DocumentNode found.

What I tried so far:

To avoid the error above I overrode Sitegeist.Taxonomy:Root to declare it as Neos.Neos:Document and see, if this would work. It does not or just a bit more. The createNew action creates a new Sitegeist.Taxonomy:Taxonomy, but it's always empty. To set properties the action needs a context which is not available since the Sitegeist.Taxonomy:Root is nowhere in the NodeTree.

Technical details:

Neos version: 8.3.9
sitegeist/taxonomy version: 1.4.0