title: Lambda expression with empty paren ()
body: <p>I came across code like:</p>
  
  <pre><code>var vpAlias = null;
  var prices = session.QueryOver&lt;Vehicle&gt;()
      .Left.JoinAlias&lt;VehiclePrice&gt;(x =&gt; x.VehiclePrice, () =&gt; vpAlias, x =&gt; x.VehiclePriceTypeId == 1)
      .Where(() =&gt; vpAlias.Id == null || vpAlias.VehiclePriceTypeId == 1)
      .Select(x =&gt; x.Id, () =&gt; vpAlias.Price)
      .ToList();
  </code></pre>
  
  <p>that uses <code>()</code> in its lambda expressions. What does that mean ? Is it used just as a placeholder ?</p>