title: No Method Error 'map' for #<Arel::Nodes::SqlLiteral>
body: <p>I have the following <strong>example</strong> query:</p>
  
  <pre><code>source = "(SELECT DISTINCT source.* FROM (SELECT * FROM items) AS source) AS items"
  items = Item.select("items.*").from(source).includes([:images])
  p items # [#&lt;Item id: 1&gt;, #&lt;Item id:2&gt;]
  </code></pre>
  
  <p>However running:</p>
  
  <pre><code>p items.count 
  </code></pre>
  
  <p>Results in <code>NoMethodError: undefined method</code>map' for Arel::Nodes::SqlLiteral`</p>
  
  <p>I appreciate the query is silly, however the non-simplifieid query is a bit too complicated to copy and this was the smallest crashing version I could create. Any ideas?</p>