code: func cachedMachineState(machID string) (ms *machine.MachineState) {
  	if machineStates == nil {
  		machineStates = make(map[string]*machine.MachineState)
  		ms, err := cAPI.Machines()
  		if err != nil {
  			return nil
  		}
  		for i, m := range ms {
  			machineStates[m.ID] = &ms[i]
  		}
  	}
  	return machineStates[machID]
  }
docs: // cachedMachineState makes a best-effort to retrieve the MachineState of the given machine ID.
  // It memoizes MachineState information for the life of a fleetctl invocation.
  // Any error encountered retrieving the list of machines is ignored.