Context Menu error : Given component must have debug id specified.

Vaadin 6 / 7 / 8 Framework UI
1

I’ tring to connect The ContextMenu object to my Tree.
When I click the right mouse button and I try to attach the ContextMenu I get an error :
Given component must have debug id specified.
What does it mean?
How can I solve it ?
Tks
Tullio