Unable-to-cast-object-error-when-converting-ATR-to-a-double

CODE:

using WealthLab.Backtest;
using System;
using WealthLab.Core;
using WealthLab.Data;
using WealthLab.Indicators;
using System.Collections.Generic;

namespace WealthScript1 
{
    public class MyStrategy : UserStrategyBase
    {
        //create indicators and other objects here, this is executed prior to the main trading loop
        public override void Initialize(BarHistory bars)
        {
         double X = ATR.Series(bars, 20).LastValue;
         double NumATRs = 1.2;
         WriteToDebugLog(X *NumATRs);
         double Shift = NumATRs * X;
        }

        //execute the strategy rules here, this is executed once for each bar in the backtest history
        public override void Execute(BarHistory bars, int idx)
        {
            if (!HasOpenPosition(bars, PositionType.Long))
            {
                //code your buy conditions here
            }
            else
            {
                //code your sell conditions here
            }
        }

        //declare private variables below

    }
}
[code]

Output:

[code]
---Symbol by Symbol Debug Logs---
---SPY---
8.13948694454827