PVS-Studio warning V510 for WildMagic5

void Terrain::LoadHeader (const std::string& heightName)
{
  ....
  std::string fileName = heightName + ".wmhf";
  FileIO header(fileName, mMode);
  assertion(header, "Cannot open file %s\n", fileName);
  ....
}

This suspicious code was found in WildMagic5 project by PVS-Studio static code analyzer.
Warning message is:
V510 The 'Assert' function is not expected to receive class-type variable as fifth actual argument. wm5terrain.cpp 150

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