Using udf is throwing classNotFoundException in scala

Question

I am using UDF with a simple function:

val upper: String => String = _.toUpperCase
import org.apache.spark.sql.functions.udf
val upperUDF = udf(upper)
dataset.withColumn("upper", upperUDF(col('text')).show

But getting the following exception:

java.lang.ClassNotFoundException: $line20.$read$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$iw$$anonfun$4 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:348) at org.apache.spark.serializer.JavaDeserializationStream$$anon$1.resolveClass(JavaSerializer.scala:67) at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1859) at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1745) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2033) at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1567) at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:2278) at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:2202) at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:2060) at