Trying to get MACD Histogram to work but getting error

[unpronounceable1700]

I'm just trying to add a MACD Histogram to my strategy. I know I'm not doing it right, but this is just from the best of my memory of how it should be done.

This is on a lower timeframe chart with 30 minute MACD added

Strategy
{
private Series <double> signal;
private Series <double> macdhistogram;


else if (State == State.Configure)
{
AddDataSeries(Data.BarsPeriodType.Minute, 30);
}

protected override void OnBarUpdate()
{

if (CurrentBar < BarsRequiredToTrade)
return;

if (BarsInProgress == 1)
{

signal[0] = EMA(MACD(BarsArray[1], 12, 26, 9), 9)[0];
macdhistogram[0] = (MACD(BarsArray[1], 12, 26, 9)[0] - signal[0]);

Print(string.Format("{0};{1};{2};{3};{4};{5};{6}", Time[0], Open[0], High[0], Low[0], Close[0], Position.MarketPosition, macdhistogram[0]));

//Longafter
if (((macdhistogram[0] - macdhistogram[1]) > 0) && ((ToTime(Time[0]) > 010000 && ToTime(Time[0]) < 080000)) || ((ToTime(Time[0]) > 170000 && ToTime(Time[0]) < 230000)) && Position.MarketPosition != MarketPosition.Long)
{
EnterLong("Longafter");
}

--------------

But I keep getting an error of Error on calling 'OnBarUpdate' method on bar 314: Object reference not set to an instance of an object.

[NinjaTrader_ChelseaB]

Hello unpronounceable1700,

In the scope of the class:

private EMA     myEMA;
private MACD  myMACD;

In OnStateChange():

else if (State == State.Configure)
{
AddDataSeries(Data.BarsPeriodType.Minute, 30);
}​
else if (State == State.DataLoaded)
{
myMACD  = MACD(BarsArray[1], 12, 26, 9);
myEMA     = EMA(myMACD, 9);
}

In OnBarUpdate():

Print(string.Format("{0} | myMACD.Diff[0]: {1}, myEMA[0]: {1}", Time[0], myMACD.Diff[0], myEMA[0]));

if (myMACD.Diff[0] - myMACD.Diff[1] > 0 && ((ToTime(Time[0]) > 010000 && ToTime(Time[0]) < 080000)) || ((ToTime(Time[0]) > 170000 && ToTime(Time[0]) < 230000)) && Position.MarketPosition != MarketPosition.Long)