title: List<T> is non nullable?
body: <p>Using VS 2022, .Net 6.0, I thought this was correct :</p>
  <pre><code>public static void test(List&lt;String&gt; list = null)
  { }
  </code></pre>
  <p>but compiler warns me :</p>
  <blockquote>
  <pre><code>CS8625 Cannot convert null literal to non-nullable reference type
  </code></pre>
  </blockquote>
  <p><code>List&lt;T&gt;</code> should be nullable by definition, right?</p>