code: def GetMostRecentClient(client_list, token=None):
    
    last = rdfvalue.RDFDatetime(0)
    client_urn = None
    for client in aff4.FACTORY.MultiOpen(client_list, token=token):
      client_last = client.Get(client.Schema.LAST)
      if client_last > last:
        last = client_last
        client_urn = client.urn
    return client_urn
docs: Return most recent client from list of clients.