I would expect, for consistency sake, that when a value list is unassigned for any reason (broken or just missed) that the XML DDR would express the errant condition it in the same way. It currently does not work that way.
Broken value list can only be found in a XML DDR when they have been broken by deleting the associated value list. When a control just has not been assigned a value list in inspector it is not easy to find in the XML DDR. Broken value list definitions where the value list has been assigned then deleted can be found by in the ValueList element where name attribute is empty. <ValueList name="" id="1"/>
when the association is simply not made the <ValueList> attribute is missing making it difficult to find in a text editor.
How to replicate
Create a file with 1 table and 1 text field in that table.
Set the UI control to any type that can be attached to a value list but do not assign one.
Run an XML DDR, look at the UI Controls definition and you will NOT see any associated value list attributes.
The value list for the control is undefined.
Create a value list.
Set the UI control to the value list, save the layout, delete the value list, and run an XML DDR.
You will see <ValueList name="" id="1"/> in the UI control definition.
Does this indicate that a value list is linked to a UI control by a name attribute instead of an ID?