face-detect-service input no-face image without Exception

[verigle]

Is your feature request related to a problem? Please describe.
why face-detect-service will return exception msg if input no-face image

Describe the solution you'd like
return the same struct with empty list of result if image has no face.

{
  "result" : [],
  "plugins_versions" : {
    "age" : "agegender.AgeDetector",
    "gender" : "agegender.GenderDetector",
    "detector" : "facenet.FaceDetector",
    "calculator" : "facenet.Calculator",
    "mask": "facemask.MaskDetector"
  }
}

Describe alternatives you've considered
other rest api should also consider this problem

Additional context