title: Using map in liquid templates
body: <p>I recently upgraded Jekyll, and <code>map</code> doesn't seem to work in my liquid templates anymore. Before I had</p>
  
  <pre><code>{{ page.categories | map: "capitalize" | join ", " }}
  </code></pre>
  
  <p>which worked as expected, producing</p>
  
  <pre><code>Programming, Ember, d3
  </code></pre>
  
  <p>but now it produces</p>
  
  <pre><code> , ,
  </code></pre>
  
  <p>There is a <code>array_to_sentence_string</code> function included in Jekyll, but this doesn't capitalize the categories. </p>
  
  <p>Has anybody else run into this problem?</p>