Steps to reproduce

1.  on 6.2.7 nightly build, open /travel/contact page
2.  go and edit any form input field, e.g. Subject

Expected results

The form opens without errors and available validators are populated in the TwinColSelect component according to configuration at /modules/form/config/validators

Actual results

A runtime error is thrown, form opens but validators are not populated

java.lang.IllegalArgumentException: Hierarchical data provider doesn't support non-hierarchical queries at com.vaadin.data.provider.HierarchicalDataProvider.size(HierarchicalDataProvider.java:51)

Development notes

Works in 6.2.6 (see demo). Found out during QA of MGNLFORM-322 but seems unrelated.

The underlying DataProvider is HierarchicalJcrDataProvider but a plain Query object is instantiated at com.vaadin.data.provider.DataCommunicator.getDataProviderSize line #815