Creating a custom class with interface returns "Crashed in OnStart with NullReferenceException: Object reference not set to an instance of an object"

Dear, 

I'm trying to create a custom class to manage the current status of open positions.  For that it needs the cAlgo.API.Position class.

public class NewcBot2 : Robot   //regular bot class
    {
        public static string sn = "CN50";
        protected override void OnStart()
        {
            PositionStatus ini = new PositionStatus();  //creates an instance of PositionStatus class
            MessageBox.Show(ini.ListIdPrice()[0].ToString()); //Attempts to show the first value of ListIdPrice method, in PositionStatus class
        }
    }

public class PositionStatus : NewcBot2 //Class Positionstatus with NewcBot2 as interface, 
    {

        public List<KeyValuePair<double, double>> ListIndexPrice()   //all this 
        {
            Dictionary<double, double> positionsdictionary = new Dictionary<double, double>();

            int i = 0;
            foreach (var position in Positions) //Positions here is from cAlgo.Api.Positions, if I remove the : NewcBot2 interface Visual Studio 2022 returns that "Positions is a type, which is not valid in the current context"
            {
                if (position.SymbolName == sn)
                {
                    positionsdictionary.Add(i, position.EntryPrice);
                }

                i++;

            }
            List<KeyValuePair<double, double>> list = positionsdictionary.ToList();
            return list;

        }

    }