title: Pandas: Select rows that are null or earlier than today?
body: <p>I have to implement the equivalent of the following SQL in a Pandas dataframe:</p>
  
  <pre><code>select * from table where ISNULL(date, GETDATE()) &gt;= as_of_date
  </code></pre>
  
  <p>Basically, I want to select the rows where the value of date is more than <code>as_of_date</code>. There are some rows where date is <code>null</code>, and in those cases, I want to only select those rows if as_of_date is less than or equal to today's date.</p>
  
  <p>Is there a way to do this in Pandas?</p>