LinkList Node In Kotlin with Helper Functions

Node.kt

class Node<T>(var value : T, var next : Node<T>? = null){

    override fun toString():String{
        val result = StringBuilder()
        var next = this.next
        result.append(value)
        while(next != null){
            result.append(", ")
            result.append(next.value)
            next = next.next
        }
        return result.toString()
    }

    fun reverse():Node<T>?{
        var prev : Node<T>? = null
        var curr : Node<T>?= this
        var next : Node<T>? = null
        while (curr != null){
            next = curr.next
            curr.next = prev
            prev = curr
            curr = next
        }
        return prev
    }

    fun forEach(unit:(T)->Unit){
        var tmpNext : Node<T>?= this.next
        unit(value)
        while(tmpNext != null){
            unit(tmpNext.value)
            tmpNext = tmpNext.next
        }

    }

    fun size():Int{
        var i = 1
        forEach{
            i++
        }
        return i
    }

    companion object{
        fun <T> of(initial : T, vararg values : T) : Node<T>{
            val result = Node(initial)
            var next : Node<T>? = null
            values.forEach{
                if(next == null){
                    next = Node(it)
                    result.next = next
                } else{
                    next?.next = Node(it)
                    next = next?.next
                }

            }
            return result
        }
    }
}