title: Pandas remove null values when to_json
body: <p>i have  actually a pandas dataframe and i want to save it to json format.
  From the pandas docs it says:</p>
  
  <blockquote>
    <p>Note NaN‘s, NaT‘s and None will be converted to null and datetime
    objects will be converted based on the date_format and date_unit
    parameters</p>
  </blockquote>
  
  <p>Then using the orient option <code>records</code>  i have something like this</p>
  
  <pre><code>[{"A":1,"B":4,"C":7},{"A":null,"B":5,"C":null},{"A":3,"B":null,"C":null}]
  </code></pre>
  
  <p>Is it possible to have this instead:</p>
  
  <pre><code>[{"A":1,"B":4,"C":7},{"B":5},{"A":3}]'
  </code></pre>
  
  <p>Thank you</p>