QXmlQuery: Returned result of evaluateTo ( QString * output ) in case nothing is found

In case the evaluation works ok QXmlQuery::evaluateTo ( QString * output ) returns true.
But what is the standard way to check whether something was found?
I would have expect that I could check for (!output->isEmpty()).
This does not work as output seems to contain one character which looks like ASCII 10 in case nothing was found.

Please add a line to the documentation about how to check for a result.

I check for (QXmlQuery::evaluateTo ( QString * output )) && (output->size() >1).

PS:
I would rather preffer to be able to check for !output->isEmpty() or !output->isNull()