Empty atom in Ecto changeset : <p>Why in an Ecto <code>changeset</code> method do you set the params to the default <code>:empty</code> atom?  e.g.</p>

<pre><code>def changeset(user, params \\ :empty) do
   ...
</code></pre>

<p>Does this allow you to call the changeset method with nil for params?</p>
