Add mistakenly removed case

Author: HyukjinKwon

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/csv/CSVRelation.scala

@@ -241,6 +241,8 @@ private[csv] class CsvOutputWriter(
       (row: InternalRow, ordinal: Int) =>
         params.timestampFormat.format(DateTimeUtils.toJavaTimestamp(row.getLong(ordinal)))
 
+    case udt: UserDefinedType[_] => makeConverter(udt.sqlType)
+
     case _ =>
       throw new UnsupportedOperationException(
         s"CSV data source does not support ${dataType.simpleString} data type.")