spark/scala : Convert all empty string records in a dataframe to null.

emptyToNullUdf.scala

import org.apache.spark.sql.expressions.UserDefinedFunction
import org.apache.spark.sql.functions.udf 
// Usage: df.select(df.columns.map(c => emptyToNullUdf(col(c)).alias(c)): _*)
def emptyToNull(_str: String): Option[String] = {
  _str match {
    case d if (_str == null || _str.trim.isEmpty) => None
    case _ => Some(_str)
  }
}
val emptyToNullUdf = udf(emptyToNull(_: String))

// https://stackoverflow.com/questions/34037889/apply-same-function-to-all-fields-of-spark-dataframe-row/55032886#55032886