[Form] Custom action type with composite multifield causing error message in a logs

[michaltobiasz]

Hi,
I have created a custom action for the Form container which in _cq_dialog has granite/ui/components/coral/foundation/form/multifield defined with composite set to true as I want to have more than one field.
When I add some values to the multifield I seeing in JCR that a new node is created under the form container node.
node_form_container
|- node_created_by_multfield

When I refresh the page in logs I see an Error
DefaultGetServlet No renderer for extension html, cannot render resource JcrNodeResource, type=nt:unstructured, superType=null, path=/path_to_multfield_node
It seems that because Form Container is a container and there is a try to render node created by multifield but it doesn't have a resource type.

I have setup also AEM 6.5.9 with core components 2.17.0 and checked a simple scenario. I have extended cq_dialog of the form container by new multifield with composite set to true. The same thing happens.

Is it possible to avoid this error somehow, shouldn't the form container component allow the use of composite multifield without any error messages in logs?