AutocompleteMultiFieldWidget with required=True fails

[szakitibi]

Provided plone.formwidget.autocomplete.widget.AutocompleteMultiFieldWidget does fail to validate required field.

I wanted to create a RelationList field with at least one related item. Possible the easiest way to reproduce is to:

1. Create a "dummy" Dexterity content type with plone.app.relationfield.behavior.IRelatedItems behavior enabled.
2. Go into plone.app.relationfield.behavior.py and:
   • do change relatedItems field to required=True
   • add widget AutocompleteMultiFieldWidget in the schema to relatedItems field with plone.autoform.directives

What happens:
It is possible to create a new "dummy" content with no related items at all.

Expected behavior:
Not be able to create "dummy" unless there is at least one related items set.

Note:
Maybe the problem is much deeper, since I'm able to create the "dummy" without step 2. I'm also not getting validation error if I go TTW:

• Dexterity Content Types > Add new content type > "Fruits"
• Add new field > "Fruits" + MultiChoice + required checked
• "Fruits" settings > values: apples, oranges

• create a new "Fruits" with no fruits selected ...

[szakitibi]

Note 2: I do now about the min_length for (Relation)List fields providing IMinMaxLength.

Maybe it is my logic which works the opposite, but I think:

• required=True with no min_length set, should not create with no value ([]), instead it should raise validation error
• while required=False with min_length=3 should set None and not raise to short validation error, unless there is one or two items selected