title: Date_add function returning None
body: <p>I have a column in a <code>dataframe1</code> that has date <code>today_date</code> and i have another <code>dataframe2</code> that has <code>days</code> along with other columns.. I am converting these two dataframes into a temptable</p>
  
  <p>I need to join <code>dataframe1</code> with <code>dataframe2</code> on one column and then add <code>today_date</code> with <code>days</code>. I am using <code>sqlcontext</code> to query these two temp tables</p>
  
  <p>I am currently using <code>date_add</code> function.</p>
  
  <pre><code>sqlcontext.sql("select date_add(today_date,days) as 'Future_date' from dataframe1 x1 join dataframe2 x2 on x1.a=x2.a"
  </code></pre>
  
  <p>However, it is returning None value in the future_date. The hive version that am using is pretty old... am running this code in <code>pyspark</code>...</p>
  
  <p>Any help is much appreciated..</p>
  
  <p>Note: I converted the <code>days</code> function from <code>unicode</code> to <code>int</code> using</p>
  
  <pre><code>dataframe2['days']=dataframe2['days'].astype(int)
  </code></pre>