What's fron with referencing the indicator?

I want to reference to DEMA indicator in my robot, but I don't understand why I can't do that.

Indicator is working, I reference it in the robot, I declare it, but it's not recognized.

I know it is super simple question, but pls help someone.

Indicator:

using System;
using cAlgo.API;
using cAlgo.API.Indicators;

namespace cAlgo.Indicators
{
    [Indicator(IsOverlay = true)]
    public class DEMA : Indicator
    {
        [Parameter]
        public DataSeries DataSource { get; set; }
        
        [Output("DEMA",Color = Colors.Yellow)]
        public IndicatorDataSeries dema { get; set; }

        [Parameter(DefaultValue = 14)]
        public int Period { get; set; }

        private ExponentialMovingAverage ema;
        private ExponentialMovingAverage ema2;
        
        protected override void Initialize()
        {
            ema = Indicators.ExponentialMovingAverage(DataSource,Period);//i need the correct DataSeries
            ema2 = Indicators.ExponentialMovingAverage(ema.Result,Period);
        }
        
        public override void Calculate(int index)
        {
           dema[index] = (2* ema.Result[index] - ema2.Result[index]);
        }
    }
}