title: Open Generic types won't register in the catalog
body: <p>We're using .NET 4.5 and have had no problem with open generic exports in MEF up until a month ago when it suddenly stopped working. 70 tests on our CI server turned red and we traced it down to missing parts in the container.</p>
  
  <p>I found it strange, so I wrote this test code:</p>
  
  <pre><code>var catalog = new TypeCatalog(typeof(Impersonator&lt;&gt;), typeof(Cache&lt;&gt;));
  var parts = catalog.Parts;
  </code></pre>
  
  <p>But it looks like none of the open generic types will register in the catalog.  <code>Parts</code> is a <code>TypeCatalog</code> with <code>Types = &lt;Empty&gt;</code>.</p>
  
  <p>Usually we go about this by declarative exports using attributes as in <a href="https://stackoverflow.com/questions/9295310/export-generics-in-mef">this SO question</a>, but none of the alternatives seems to be working anymore.</p>
  
  <p>Any idea will be most appreciated.</p>