title: How can I specify null in an xaml element (eg when passing to a collection of nullable types)
body: <p>I have a WPF IValueConverter that I've written. I plan to use it in a number of places.
  It has a public property that is a collection of nullable DateTumes. i.e. List
  eg</p>
  
  <pre><code>private List&lt;DateTime?&gt; _dates = new List&lt;DateTime?&gt;();
  public List&lt;DateTime?&gt; Dates 
  { 
    get { return _dates; }
    set { _dates = value; }
  }
  </code></pre>
  
  <p>How can I pass it a set of values in XAML, including a null value?</p>
  
  <p>My attempts were</p>
  
  <pre><code>&lt;myns:MyConverter x:key="MyName"&gt;
    &lt;myns:MyConverter.Dates&gt;
      &lt;sys:DateTime&gt;1 Jan 2014&lt;/sys:DateTime&gt; &lt;!-- this works --&gt;
      &lt;sys:DateTime /&gt; &lt;!-- unf this comes through as 1 Jan 0001 --&gt;
      &lt;sys:DateTime? /&gt; &lt;!-- invalid syntax with the ? character --&gt;
    &lt;/myns:MyConverter.Dates&gt;
  &lt;/myns:MyConverter&gt;
  </code></pre>