Why does this code fail with Ecto.NoPrimaryKeyValueError
<p>Why does this fail: </p>

<pre><code>%Partner{} |&gt; cast(%{id: 123}, [:id]) |&gt; delete 
</code></pre>

<p>with a <code>Ecto.NoPrimaryKeyValueError</code>? I'm setting the primary key explicitly?</p>