title: Throwing exceptions in getters and setters
body: <p>I was wondering what the best practice is for model validation when it comes to using getters and setters. Specifically, I have nullable fields in my model that, in some use cases, should not have null values when accessed. In those cases, I would like to throw an exception from the getter, but is that an accepted practice?</p>
  
  <p>This could also be the case if I received a value in a setter that was not valid.</p>
  
  <p>Alternatively from throwing exceptions, I'm aware of MVC attributes that you can use to decorate fields, but have not used them very much for model validation. In the "This value shouldn't be null in my getter" scenario, is there an appropriate attribute I could use?</p>
  
  <p>Also, if throwing exceptions in getters and setters is accepted, is there a recommended exception to throw, i.e. ValueNotValidException (if that were real)?</p>