title: Date column returning number if NA is precent
body: <p>I am trying to incorporate date in a column. But it is returning number since NA is present. Can anyone help me?</p>
  <pre><code>asdd &lt;- data.frame(a = c(NA,as.Date(today(),&quot;%m/%d/%Y&quot;)), b = c(2,3))
  asdd
        a b
  1    NA 2
  2 19220 3
  </code></pre>
  <p>i want get as Date in the column?</p>