Did you tested it ?

bool ContactGroupTool::convertToXml(const ContactGroup &group, QIODevice *device, QString *errorMessage)
{
    Q_UNUSED(errorMessage);

    XmlContactGroupWriter writer;
    writer.write(group, device);

    return true;
}

errorMessage was never used. So you will report an empty string.

What is the test case for this bug ?

why creating a errorMessage ?

In D25213#560009, @mlaurent wrote:

Did you tested it ?

bool ContactGroupTool::convertToXml(const ContactGroup &group, QIODevice *device, QString *errorMessage)
 {
     Q_UNUSED(errorMessage);
 
     XmlContactGroupWriter writer;
     writer.write(group, device);
 
     return true;
 }

errorMessage was never used. So you will report an empty string.

What is the test case for this bug ?

So if the method never fail we should probably add this quite useful information in the doc and add a TODO KF6 to change the method signature