clicking on legend causes Unexpected null value charts_flutter - flutter

Question

When I click on a specific item in the legend like '1 week out (25)' the chart goes red and gives an error Unexpected null value. The relevant error-causing widget was BarChart. I don't even need the legend to be clickable, but I don't see an override to the callback that's happening here. Desired output is that the legend is not clickable, or the legend is clickable, but the UI doesn't bug out when selecting a specific legend item. Cheers!
import 'package:flutter/material.dart';
import 'package:charts_flutter/flutter.dart' as charts;
class StackedHorizontalBarChartCurrentCapacity extends StatelessWidget {
final List<charts.Series> seriesList;
final bool animate;
final CapableShop capableShop;
StackedHorizontalBarChartCurrentCapacity(this.seriesList, this.capableShop,
{this.animate});
factory StackedHorizontalBarChartCurrentCapacity.withCurrentCapacityEnrouteData(
CapableShop capableShop) {
return new StackedHorizontalBarChartCurrentCapacity(
_createCurrentCapacityEnrouteData(
currentEnroute: capableShop.currentEnroute,
currentEnrouteOptimal: capableShop.currentEnrouteOptimal,
currentEnrouteWeek1: capableShop.currentEnrouteWeek1,
currentEnrouteWeek2: capableShop.currentEnrouteWeek2,
currentEnrouteWeek3: capableShop.currentEnrouteWeek3,
currentEnrouteWeek3plus: capableShop.currentEnrouteWeek3plus,
currentFlexMax: capableShop.currentFlexMax,
currentOptimal: capableShop.currentOptimal),
capableShop,
animate: false,
);
}
#override
Widget build(BuildContext context) {
// print(capableShop.toJson());
return new charts.BarChart(
seriesList,
animate: animate,
barGroupingType: charts.BarGroupingType.stacked,
vertical: false,
behaviors: [
new charts.SeriesLegend(
desiredMaxColumns: 2,
cellPadding: EdgeInsets.all(2),
showMeasures: true,
desiredMaxRows: 3,
position: charts.BehaviorPosition.top,
horizontalFirst: false,
measureFormatter: (measure) => "(" + measure.toString() + ")",
legendDefaultMeasure: charts.LegendDefaultMeasure.firstValue,
)
],
primaryMeasureAxis: new charts.NumericAxisSpec(
renderSpec: charts.SmallTickRendererSpec(
minimumPaddingBetweenLabelsPx: 0,
labelAnchor: charts.TickLabelAnchor.after,
labelStyle: charts.TextStyleSpec(
fontSize: 10,
),
labelRotation: 30,
lineStyle:
charts.LineStyleSpec(color: charts.MaterialPalette.black)),
tickProviderSpec: charts.StaticNumericTickProviderSpec([
charts.TickSpec(capableShop.currentOptimal,
label: capableShop.currentOptimal.toString() + ' Optimal'),
charts.TickSpec(capableShop.currentFlexMax,
label: capableShop.currentFlexMax.toString() + ' Flex Max'),
charts.TickSpec(capableShop.currentEnrouteOptimal,
label: capableShop.currentEnrouteOptimal.toString() +
' Enroute Optimal'),
]),
viewport:
charts.NumericExtents(0, capableShop.currentEnrouteOptimal)),
);
}
static List<charts.Series<ChartAmount, String>>
_createCurrentCapacityEnrouteData({
int currentEnroute,
int currentEnrouteWeek1,
int currentEnrouteWeek2,
int currentEnrouteWeek3,
int currentEnrouteWeek3plus,
int currentFlexMax,
int currentOptimal,
int currentEnrouteOptimal,
}) {
final canonicalEnroute = [
new ChartAmount(
"${currentEnroute ?? 10} Canonical Enroute", currentEnroute ?? 10),
];
final oneWeekOut = [
new ChartAmount(
"${(currentEnrouteWeek1 ?? 2) + (currentEnrouteWeek2 ?? 3) + (currentEnrouteWeek3 ?? 1) + (currentEnrouteWeek3plus ?? 1)} AVSO Enroute",
currentEnrouteWeek1 ?? 2),
];
final twoWeeksOut = [
new ChartAmount(
"${(currentEnrouteWeek1 ?? 2) + (currentEnrouteWeek2 ?? 3) + (currentEnrouteWeek3 ?? 1) + (currentEnrouteWeek3plus ?? 1)} AVSO Enroute",
currentEnrouteWeek2 ?? 3),
];
final threeWeeksOut = [
new ChartAmount(
"${(currentEnrouteWeek1 ?? 2) + (currentEnrouteWeek2 ?? 3) + (currentEnrouteWeek3 ?? 1) + (currentEnrouteWeek3plus ?? 1)} AVSO Enroute",
currentEnrouteWeek3 ?? 1),
];
final plus = [
new ChartAmount(
"${(currentEnrouteWeek1 ?? 2) + (currentEnrouteWeek2 ?? 3) + (currentEnrouteWeek3 ?? 1) + (currentEnrouteWeek3plus ?? 1)} AVSO Enroute",
currentEnrouteWeek3plus ?? 1),
];
return [
new charts.Series<ChartAmount, String>(
id: '1 Week Out',
domainFn: (ChartAmount amount, _) => amount.label,
measureFn: (ChartAmount amount, _) => amount.enroute,
data: oneWeekOut,
measureUpperBoundFn: (_, __) => currentEnrouteOptimal,
measureLowerBoundFn: (_, __) => 0,
),
new charts.Series<ChartAmount, String>(
id: '2 Weeks Out',
domainFn: (ChartAmount amount, _) => amount.label,
measureFn: (ChartAmount amount, _) => amount.enroute,
data: twoWeeksOut,
measureUpperBoundFn: (_, __) => currentEnrouteOptimal,
measureLowerBoundFn: (_, __) => 0,
),
new charts.Series<ChartAmount, String>(
id: '3 Weeks Out',
domainFn: (ChartAmount amount, _) => amount.label,
measureFn: (ChartAmount amount, _) => amount.enroute,
data: threeWeeksOut,
measureUpperBoundFn: (_, __) => currentEnrouteOptimal,
measureLowerBoundFn: (_, __) => 0,
),
new charts.Series<ChartAmount, String>(
id: '3+ Weeks Out',
domainFn: (ChartAmount amount, _) => amount.label,
measureFn: (ChartAmount amount, _) => amount.enroute,
data: plus,
measureUpperBoundFn: (_, __) => currentEnrouteOptimal,
measureLowerBoundFn: (_, __) => 0,
),
new charts.Series<ChartAmount, String>(
id: 'Canonical Enroute',
domainFn: (ChartAmount amount, _) => amount.label,
measureFn: (ChartAmount amount, _) => amount.enroute,
data: canonicalEnroute,
measureUpperBoundFn: (_, __) => currentEnrouteOptimal,
measureLowerBoundFn: (_, __) => 0,
colorFn: (datum, index) =>
charts.ColorUtil.fromDartColor(Colors.blue[800]),
),
];
}
}