Validate in doWork method

DoWorkValidate.kt

doWork() : Result<Email> {
  ...
  validate() elseIf {
    InvalidEmailAddress { errorMessage: String -> 
      return Failure(errorMessage)
    }
    EmptySubject { errorMessage: String -> /* handle failure */ }
    EmptyBody { errorMessage: String -> /* handle failure */ }
  }
  ...
}