Replace all ":" with "_" in Spark dataframe
<p>I'm trying to replace all instances of ":" --> "_" in a single column of a Spark dataframe. I'm trying to do this with:</p>

<pre><code>val url_cleaner = (s:String) =&gt; {
   s.replaceAll(":","_")
}
val url_cleaner_udf = udf(url_cleaner)
val df = old_df.withColumn("newCol", url_cleaner_udf(old_df("oldCol")) )
</code></pre>

<p>But I keep getting the error:</p>

<pre><code> SparkException: Job aborted due to stage failure: Task 0 in stage 25.0 failed 4 times, most recent failure: Lost task 0.3 in stage 25.0 (TID 692, ip-10-81-194-29.ec2.internal): java.lang.NullPointerException
</code></pre>

<p>Where am I going wrong in the udf?</p>