title: ASP.NET WebAPI Routing Issue
body: <p>Say I have the following actions;</p>
  
  <pre><code>// api/products
  public IEnumerable&lt;ProductDto&gt; GetProducts()
  public ProductDto GetProduct(int id)
  
  // api/products/{productId}/covers
  public IEnumerable&lt;CoverDto&gt; GetCovers(int productId)
  </code></pre>
  
  <p><strong>What would be the best way to create a route to use as a shortcut to a "master" product?</strong> i.e. <code>api/products/master</code></p>
  
  <p>I've tried adding a master controller, and routing the above to it, but I get the following error:</p>
  
  <pre><code>The parameters dictionary contains a null entry for parameter 'id' 
  of non-nullable type 'System.Int32' for method 'ProductDto GetProduct(Int32)' 
  in 'ProductsController'. An optional parameter must be a reference type, 
  a nullable type, or be declared as an optional parameter.
  </code></pre>
  
  <p>To fix this, I've tried updating the normal product route to <code>api/products/{id:int}</code>, but to no avail.</p>
  
  <p>I would like to end up with the following; where the only difference is that the "master" product would be obtained by a <em>code</em>, not an id</p>
  
  <pre><code>api/products
  api/products/1
  api/products/1/covers
  api/products/master
  api/products/master/covers
  </code></pre>