docs: def ProcessLegacyClient(self, ping, client):
      """Update counters for system, version and release attributes."""
      labels = self._GetClientLabelsList(client)
      system = client.Get(client.Schema.SYSTEM, "Unknown")
      uname = client.Get(client.Schema.UNAME, "Unknown")
  
      self._Process(labels, ping, system, uname)