How do I fix this NoSuchMethodError inFlutter? - flutter

Question

I am following along with an online course yet my code throws an error where the instructor's code doesn't. Yes, I've scanned over it to make sure they are identical.
Maybe there is some small detail I've missed. At any rate, can someone please help me fix this error so I can move on?
Here is the get method:
List<Map<String, Object>> get groupedTransactionValues {
return List.generate(7, (index) {
final weekDay = DateTime.now().subtract(
Duration(days: index),
);
var totalSum = 0.0;
for (int i; i < recentTransactions.length; i++) {
if (recentTransactions[i].date.day == weekDay.day &&
recentTransactions[i].date.month == weekDay.month &&
recentTransactions[i].date.year == weekDay.year) {
totalSum += recentTransactions[i].amount;
}
}
return {
'day': DateFormat.E().format(weekDay).substring(0, 1),
'amount': totalSum,
};
});
}
And here is the implementation of it in Flutter:
#override
Widget build(BuildContext context) {
return Card(
elevation: 6,
margin: EdgeInsets.all(20),
child: Row(
children: groupedTransactionValues.map((data) {
}).toList(),
),
);
}
}
And here's the error message:
The following NoSuchMethodError was thrown building Chart(dirty):
The method '<' was called on null.
Receiver: null
Tried calling: <(0)
When the exception was thrown, this was the stack:
#0 Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1 Chart.groupedTransactionValues.<anonymous closure>
package:expense/widgets/chart.dart:19
#2 new List.generate (dart:core-patch/array_patch.dart:78:28)
#3 Chart.groupedTransactionValues
package:expense/widgets/chart.dart:13
#4 Chart.build
package:expense/widgets/chart.dart:45
#5 StatelessElement.build
package:flutter/…/widgets/framework.dart:4620
#6 ComponentElement.performRebuild
package:flutter/…/widgets/framework.dart:4546
#7 Element.rebuild
package:flutter/…/widgets/framework.dart:4262
#8 ComponentElement._firstBuild
package:flutter/…/widgets/framework.dart:4525
#9 ComponentElement.mount
package:flutter/…/widgets/framework.dart:4520
#10 Element.inflateWidget
package:flutter/…/widgets/framework.dart:3490
#11 MultiChildRenderObjectElement.mount
package:flutter/…/widgets/framework.dart:5991
... Normal element mounting (109 frames)
#120 Element.inflateWidget
package:flutter/…/widgets/framework.dart:3490
#121 MultiChildRenderObjectElement.mount
package:flutter/…/widgets/framework.dart:5991
... Normal element mounting (210 frames)
#331 Element.inflateWidget
package:flutter/…/widgets/framework.dart:3490
#332 MultiChildRenderObjectElement.mount
package:flutter/…/widgets/framework.dart:5991
... Normal element mounting (273 frames)
#605 Element.inflateWidget
package:flutter/…/widgets/framework.dart:3490
#606 Element.updateChild
package:flutter/…/widgets/framework.dart:3258
#607 RenderObjectToWidgetElement._rebuild
package:flutter/…/widgets/binding.dart:1174
#608 RenderObjectToWidgetElement.mount
package:flutter/…/widgets/binding.dart:1145
#609 RenderObjectToWidgetAdapter.attachToRenderTree.<anonymous closure>
package:flutter/…/widgets/binding.dart:1087
#610 BuildOwner.buildScope
package:flutter/…/widgets/framework.dart:2620
#611 RenderObjectToWidgetAdapter.attachToRenderTree
package:flutter/…/widgets/binding.dart:1086
#612 WidgetsBinding.attachRootWidget
package:flutter/…/widgets/binding.dart:927
#613 WidgetsBinding.scheduleAttachRootWidget.<anonymous closure>
package:flutter/…/widgets/binding.dart:908
(elided 11 frames from class _RawReceivePortImpl, class _Timer, dart:async, and dart:async-patch)

Answer 1

for (int i; i < recentTransactions.length; i++) {
This is the part causing the Error, since it is stated: "The method '<' was called on null." You have to initalise your int i = 0, so the code should look like
for (int i = 0; i < recentTransactions.length; i++) {