null pointers because of the null return when there is no combination, but fine

HowSum.scala

object HowSum extends App {

  def howSum(n: Int, coins: Array[Int]): Array[Int] = {

    if (n == 0) return Array[Int]()
    if (n < 0) return null

    for (coin <- coins) {
      val rest = n - coin
      val ints = howSum(rest, coins)
      if (ints != null)
        return Array.concat(Array[Int](coin), ints)
    }

    null
  }


  println(howSum(0, Array[Int](7)).mkString(","))
  println(howSum(7, Array[Int](7)).mkString(","))
  println(howSum(7, Array[Int](1)).mkString(","))
  println(howSum(7, Array[Int](1, 7)).mkString(","))
  println(howSum(7, Array[Int]( 2, 3, 8, 7)).mkString(","))
  println()
  println(howSum(300, Array[Int](7, 14)).mkString(","))
  println(howSum(7, Array[Int](8)).mkString(","))
  println(howSum(7, Array[Int](8, 7)).mkString(","))
  println(howSum(7, Array[Int](5, 3, 4, 7)).mkString(","))
}