Spark : java.lang.NoClassDefFoundError: scala/collection/mutable/ArraySeq$ofRef

I am trying to run a simple word count program with spark-submit and getting an exception.

Exception in thread "main" java.lang.BootstrapMethodError: java.lang.NoClassDefFoundError: scala/collection/mutable/ArraySeq$ofRef at SparkWordCount$.main(SparkWordCount.scala:18)

The code, starting with line 18 is

val count = input.flatMap(line ⇒ line.split(" "))
    .map(word ⇒ (word, 1))
    .reduceByKey(_ + _)

My environment:

• Windows 10
• java version "1.8.0_221"
• spark-shell shows : Spark version 2.4.4 (Using Scala version 2.11.12)
• scala -version command shows Scala code runner version 2.13.1

As stated in the comments, the solution is to use for development the same version of Scala that you will use on the cluster.