QXmlQuery setFocus

[redlars]

Hello,
The setFocus call below causes "Stopped in thread 0 by: Exception at 0x7c812aeb, Code: 0xe06d7363: C++ exception".
@
bool MyClass::OnFinished(QNetworkReply* reply)
{
QXmlQuery query;
query.setFocus(reply);
}
@

The method is triggerd by QNetworkAccessManager::finished signal and the reply does not contain any errors.

What am I doing wrong in this case?

Using Qt 4.7.1