Handle User not found issue

[hossain-khan]

https://github.com/some-random-user-xyz

{
  "message": "Validation Failed",
  "errors": [
    {
      "message": "The listed users cannot be searched either because the users do not exist or you do not have permission to view the users.",
      "resource": "Search",
      "field": "q",
      "code": "invalid"
    }
  ],
  "documentation_url": "https://docs.github.com/v3/search/",
  "status": "422"
}