title: 304 response with Owin
body: <p>Whats the correct way of doing a 304 response with Owin middleware?</p>
  
  <p>I'm doing this</p>
  
  <pre><code>public override Task Invoke(IOwinContext context)
  {
      var response = context.Response;
      response.ContentType = "application/javascript";
      response.StatusCode = 200;
  
      if (ClientCached(context.Request, scriptBuildDate))
      {
          response.StatusCode = 304;
          response.Headers["Content-Length"] = "0";
          return null;
      }
      response.Headers["Last-Modified"] = scriptBuildDate.ToUniversalTime().ToString("r");
  
      return context.Response.WriteAsync(js);
  }
  </code></pre>
  
  <p>Returning <code>null</code> is that correct for empty body response? It works but I was wondering how its supposed to be setup</p>