title: Linq lambda null-coalescing a nullable int
body: <p>I have a Category Model which has a <strong>ParentID</strong> field of <strong>int?</strong> datatype.
  I'm trying to achieve this:</p>
  
  <pre><code>WHERE 
      ISNULL(ParentID,0) == ParentCategoryID
  </code></pre>
  
  <p>... in linq but seem to be struggling because it's telling me I can't apply <strong>??</strong> to ParentID as it's a nullable integer.</p>
  
  <pre><code>IList&lt;Category&gt; ChildCategories = AllCategoriesAsList
      .Where(c =&gt; c.ParentID ?? 0 == ParentCategoryID)
      .ToList();
  </code></pre>
  
  <p>I'm a bit stuck.</p>