QIdentityProxyModel has no headers when it has zero rows

From an email:

in QIdentityProxyModel there is a problem with headerData method if the
model has zero rows.
In this case no headers are shown because of the implementation of
QAbstractProxyModel::headerData and index.

I changed headerData into

in my
subclass and got rid of the problem.
I reported the problem to digia support and was told they didn't write
this class and that I should overload the index function in my subclass.