TreeViewDelegate Unable to assign QJSValue to QString

[Mihaill]

Hi!
My model for TreeView return QJsonObject .
I use TreeViewDelegate like delegate.
TreeViewDelegate return error: Unable to assign QJSValue to QString
But when my model return string, then TreeViewDelegate don't have errors.
What can I do with TreeViewDelegate? Maybe need make role in model for TreeViewDelegate?

[Mihaill]

TreeViewDelegate use model.display
This help me

contentItem: Item{}