only print the error message if there's an argument
only print the error message if there's an argument

Reviewed By: CarlaCosenza

Differential Revision: D16963059

fbshipit-source-id: 81d3a300ec6bbcd778388b0bbf67a7bf5c7add89

facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl,facebook/FBSimulatorControl