RecyclerView.Adapter- Error: public functions exposes its internal return type in Kotlin

I am implementing a RecylcerView.Adapter class in Kotlin. I am getting compile time error, see comments in following code.

// Compile time Error: 'public' function exposes its 'internal' return type ViewHolder
class DietListAdapter(context: Context, private val foodList: ArrayList<Food>) : RecyclerView.Adapter<DietListAdapter.ViewHolder>() {

    private val inflater: LayoutInflater
    private var onItemClick: Callback<Void, Int>? = null

    init {
        inflater = LayoutInflater.from(context)
    }
    // Compile time Error: 'public' function exposes its 'internal' return type ViewHolder
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): DietListAdapter.ViewHolder {
        val holder = ViewHolder(inflater.inflate(R.layout.layout_food_list_item, parent, false))
        return holder
    }
    // Compile time Error: 'public' function exposes its 'internal' parameter type ViewHolder
    override fun onBindViewHolder(holder: DietListAdapter.ViewHolder, position: Int) {
        holder.textViewFoodName.text = foodList[position].foodName
        holder.textViewFoodDesc.text = foodList[position].foodDesc

        holder.itemView.setOnClickListener {
            if (onItemClick != null)
                onItemClick!!.callback(foodList[position].foodId)
        }
    }
    ...
    ...
    internal inner class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        var textViewFoodName: TextView
        var textViewFoodDesc: TextView

        init {
            textViewFoodName = itemView.findViewById(R.id.textViewFoodName) as TextView
            textViewFoodDesc = itemView.findViewById(R.id.textViewFoodDesc) as TextView
        }
    }
    ...
    ...
}

I have checked it in Kotlin documentation, No solution.

Has anyone else faced this issue?