title: Web API - NotFound helper no ModelStateDictionary overload
body: <p>All the helpers have an overload that includes the ModelState. For example </p>
  
  <pre><code>return Conflict({YourModelState}),    
  return BadRequest({YourModelState});
  </code></pre>
  
  <p>Why for God's sake the return NotFound helper doesn't have one?</p>