title: FirstOrDefault: Default value other than null
body: <p>As I understand it, in Linq the method <code>FirstOrDefault()</code> can return a <code>Default</code> value of something other than null.  What I haven't worked out is what kind of things other than null can be returned by this (and similar) method when there are no items in the query result.  Is there any particular way that this can be set up so that if there is no value for a particular query some predefined value is returned as the default value?</p>