title: c# null for System.drawing.PoinF
body: <p>I'm using C# for grphics. And now I want to return a null for PointF</p>
  
  <pre><code>    /// &lt;summary&gt;
      /// Project the point according to camera position.
      /// &lt;/summary&gt;
      /// &lt;param name="p"&gt;Point position, in WC&lt;/param&gt;
      /// &lt;returns&gt;pixel position&lt;/returns&gt;
      public PointF Project(MCvPoint3D32f p)
      {
          //return new PointF(p.x, p.y);
          // Extend p
          Matrix&lt;double&gt; p_ex = new Matrix&lt;double&gt;(3, 1);
          p_ex[0, 0] = p.x;
          p_ex[1, 0] = p.y;
          p_ex[2, 0] = p.z;
  
          var rst = HomographMatrix * p_ex;
          rst[0, 0] = rst[0,0] / rst[2, 0] * focalLength * scale;
          rst[1, 0] = rst[1, 0] / rst[2, 0] * focalLength * scale;
  
          return new PointF((float)rst[0, 0], (float)rst[1, 0]);
      }
  </code></pre>
  
  <p>Here I want to return a 'null' for the point if the point is out of FoV of my camera. But actually PointF is not 'nullable', so is there a straight forward way to return a 'null' for the point?</p>
  
  <p>I don't want to inherit the native PointF.</p>