Cannot set Date in collective.easyform

In Plone 5.2.1 (Python 3.7.3) I have added a form with a Date field, but when I press on "Settings" of that field I get the pop-up that says "There was an error loading modal."
How can I adjust the settings of the date field?

Clearly a bug

Traceback (innermost last):

Module ZPublisher.WSGIPublisher, line 156, in transaction_pubevents
Module ZPublisher.WSGIPublisher, line 338, in publish_module
Module ZPublisher.WSGIPublisher, line 256, in publish
Module ZPublisher.mapply, line 85, in mapply
Module ZPublisher.WSGIPublisher, line 62, in call_object
Module plone.z3cform.layout, line 63, in __call__
Module plone.z3cform.layout, line 47, in update
Module plone.z3cform.fieldsets.extensible, line 65, in update
Module plone.z3cform.patch, line 30, in GroupForm_update
Module, line 132, in update
Module z3c.form.form, line 136, in updateWidgets
Module z3c.form.field, line 257, in update
Module zope.component._api, line 97, in getMultiAdapter
zope.interface.interfaces.ComponentLookupError: ((<zope.schema._bootstrapfields.Field object at 0x7fe4d6caa400>, <WSGIRequest, URL=>), <InterfaceClass z3c.form.interfaces.IFieldWidget>, '')

Please file a bug report

I do, but where and how?

Please check other issues before to avoid duplicates.