title: Dataset: what to put for blank date fields?
body: <p>I am creating a dataset by pulling information from Trello (task organizer). One column will have a date a card was moved to a list, if that event occurred. There are a few cards that were never moved to that list, so I will have some rows with no date.</p>
  
  <p>What's the correct value to put in these rows that are without a date? What is the best approach from a data management perspective so that blank fields won't affect formulas and plotting the data?</p>
  
  <p>I am working with Pandas for data analysis.</p>
  
  <p>For example, the pseudo code would run like this:</p>
  
  <pre><code>for card in list_of_cards:
      if card.location == 'DONE_LIST':
          return card.date_moved
      else:
          return None  # &lt;--- or should it be '', 'NaN', '0', ' ', or something else?
  </code></pre>