PVS-Studio warning V522 for QT

void QDocIndexFiles::readIndexSection(....)
{
  ....
  DocNode* dn = qdb_->findGroup(groupNames[i]);
  if (dn) {
    dn->addMember(node);
  }
  else {
    ....
    qDebug() << "DID NOT FIND GROUP:" << dn->name()
             << "for:" << node->name();
  }
  ....
}

This suspicious code was found in QT project by PVS-Studio static code analyzer.
Warning message is:
V522 Dereferencing of the null pointer 'dn' might take place. qdocindexfiles.cpp 539

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/