                &lt;NA&gt;</span>
<span class="co">#&gt; 4                1            open           2013-11-20                &lt;NA&gt;</span>
<span class="co">#&gt; 5                1            open           2013-11-20                &lt;NA&gt;</span>
<span class="co">#&gt; 6                1            open           2013-11-20                &lt;NA&gt;</span>
<span class="co">#&gt;   milestone_due_on n_comments created_at updated_at  closed_at</span>
<span class="co">#&gt; 1             &lt;NA&gt;  