title: How do I convert a System.Type to its nullable version?
body: <p>Once again one of those: "Is there an easier built-in way of doing things instead of my helper method?"</p>
  
  <p>So it's easy to get the underlying type from a nullable type, but how do I get the nullable version of a .NET type?</p>
  
  <p>So I have</p>
  
  <pre><code>typeof(int)
  typeof(DateTime)
  System.Type t = something;
  </code></pre>
  
  <p>and I want</p>
  
  <pre><code>int? 
  DateTime?
  </code></pre>
  
  <p>or</p>
  
  <pre><code>Nullable&lt;int&gt; (which is the same)
  if (t is primitive) then Nullable&lt;T&gt; else just T
  </code></pre>
  
  <p>Is there a built-in method?</p>