title: Possible to add udf wrapper to this dataframe operation
body: <pre><code>var result_df1 = result_df.select(result_df.columns.map(c =&gt; col(c).cast(StringType)): _ * )
  </code></pre>
  
  <p>This is my dataframe operation I am performing.  I have a udf called <code>EmptyToNull</code> that takes in one paramter, a value, checks if it is empty, if so, it changes it to null.  Is it possible to call this UDF in this dataframe operation I am already performing?</p>