title: How to simulate undefined in Dart
body: <p>In JS, there is undefined and null. Undefined means &quot;no value&quot;, null means &quot;value equivalent to emptiness&quot;.
  In Dart however (and possibly in other languages, I don't know, but right now I'm using Dart), there is no undefined, only null. Therefore it is impossible to make the distinction between a value equivalent to emptiness and the absence of value.</p>
  <p>Is there a standard way of simulating this difference in Dart?</p>