Not work on simple example

[semmaxim]

Result of this code is empty.

import com.lambdaworks.jacks.JacksMapper

class First (val num: Int, val str: String) {}
class Second (val firstClass: First, val num: Int, val str: String) {}
class Third (val firstClass: First, val secondClass: Second, val num: Int, val str: String) {}

object Program extends App{
    val first = new First(1, "first")
    val second = new Second(first, 11, "second")
    val third = new Third(first, second, 111, "third")

    println(JacksMapper.writeValueAsString(third))
}