Commented Unassigned: Cannot Override Editor Template Definition for Type [21849]

I am trying to follow the example in your documentation for defining a custom editor template based on type (not property name). When I use this example and specify

> <xctk:EditorTemplateDefinition TargetProperties="{x:Type fwdesignertree:ModelNodeReference}">

I get an error The specified value cannot be assigned. The following type was expected: "IList".

I am not sure if I am looking at old documentation or if I am doing something incorrect. Any help you can provide would be much appreciated. Thanks.
Comments: ** Comment from web user: BoucherS **

For now, do not consider this as an error. It's just a warning and it won't stop your application from working.