title: Can a non-nullable reference type in C# 8 be null in runtime?
body: <p>It seems to me there is really no guarantee that a non-nullable variable won't ever have null. Imagine I have a class that has one property that is not nullable:</p>
  
  <pre><code>public class Foo
  {
      public Foo(string test)
      {
          Test = test;
      }
      public string Test {get;set;}
  }
  </code></pre>
  
  <p>Now that might seem like it's now cannot be null. But if we reference this class with another library that does not use nullable context, nothing stops it from sending null in there.</p>
  
  <p>Is that correct or there are some runtime checks as well perhaps that ensure this?</p>