Solving the exception: The getter 'iterator' was called on null - flutter

Question

I'm trying to solve an issue where I get the runtime exception:
════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The getter 'iterator' was called on null.
Receiver: null
Tried calling: iterator
The relevant error-causing widget was:
RecordTile AndroidStudioProjects/abc/lib/screens/clinical_records_screen.dart:80:31
════════════════════════════════════════════════════════════════════════════════════════════════════
The exception is in the line:
return loading
? LoadingAnimation()
: RecordTile(
records: clinical_records,
position: position,
);
and is being generated even after I have wrapped it in a try/catch block. How do I get to the root of this? I tried checking whether an element in the list is null.
My code is as follows:
class PreviousRecordsSummaryScreen extends StatefulWidget {
static const String id = 'ClinicalRecordsScreen';
List<CheckinNew> clinical_records;
Customer customer;
PreviousRecordsSummaryScreen({
this.clinical_records,
this.customer,
});
#override
_PreviousRecordsSummaryScreenState createState() =>
_PreviousRecordsSummaryScreenState();
}
class _PreviousRecordsSummaryScreenState
extends State<PreviousRecordsSummaryScreen> {
List<CheckinNew> clinical_records;
Customer customer;
bool loading;
List<CheckinNew> sortedRecords(List<CheckinNew> initialList) {
print("Sorting by date.. newest first");
List<CheckinNew> sortList = initialList;
sortList.sort((b, a) => a.actualDate.compareTo(b.actualDate));
print(sortList); // [two, four, three]
return sortList;
}
#override
void initState() {
clinical_records = widget.clinical_records;
customer = widget.customer;
print("Customer: ${customer.name} ${customer.cstid}");
loading = false;
super.initState();
}
#override
Widget build(BuildContext context) {
print("In ClinicalRecordsScreen");
print("clinical_records is $clinical_records");
clinical_records = sortedRecords(clinical_records);
return Scaffold(
appBar: AppBar(title: Text("${widget.customer.name}'s visits")),
body: Container(
child: ListView(
shrinkWrap: true,
children: [
clinical_records == null
? Container()
: ListView.builder(
shrinkWrap: true,
itemCount: (clinical_records == null)
? 0
: clinical_records.length,
itemBuilder: (BuildContext context, int position) {
print(
"Before calling RecordTile, position:$position clinical_records:$clinical_records ");
print("Printing each element");
int index = 0;
for (CheckinNew el in clinical_records) {
print("el: $el $index");
index++;
}
try {
return loading
? LoadingAnimation()
: RecordTile(
records: clinical_records,
position: position,
);
} catch (e) {
return Container();
}
},
),
],
),
),
);
}
}
class RecordTile extends StatefulWidget {
RecordTile({
this.records,
this.position,
this.expanded = false,
});
List<CheckinNew> records;
int position;
bool expanded;
#override
_RecordTileState createState() => _RecordTileState();
}
class _RecordTileState extends State<RecordTile> {
bool expanded;
List<CheckinNew> records;
int position;
#override
void initState() {
expanded = widget.expanded;
records = widget.records;
position = widget.position;
super.initState();
}
Widget medicines(List<MedsResponse> meds) {
List<Widget> mylist = [];
for (MedsResponse presc in meds) {
print(presc.brand);
mylist.add(Divider(
height: 10,
));
mylist.add(
Wrap(
alignment: WrapAlignment.start,
crossAxisAlignment: WrapCrossAlignment.start,
children: [
CircleAvatar(
radius: 10,
backgroundColor: Colors.grey.shade800,
child: Text((meds.indexOf(presc) + 1).toString()),
),
Padding(
padding: EdgeInsets.symmetric(horizontal: 2),
),
Text(
presc.brand,
style: TextStyle(color: Colors.black),
),
],
),
);
mylist.add(
Padding(
padding: EdgeInsets.symmetric(vertical: 2),
),
);
mylist.add(
Row(
children: [
Padding(padding: EdgeInsets.symmetric(horizontal: 10)),
Text(
'${presc.dose} ${presc.unit} ${presc.freq} x ${presc.durn} ${presc.durnunit}',
style: TextStyle(color: Colors.black),
),
],
),
);
mylist.add(
Padding(
padding: EdgeInsets.symmetric(vertical: 2),
),
);
mylist.add(
Wrap(
children: [
Padding(padding: EdgeInsets.symmetric(horizontal: 10)),
Text(
'(${presc.generic})',
style: TextStyle(
color: Colors.black,
),
),
],
),
);
mylist.add(
Padding(
padding: EdgeInsets.symmetric(vertical: 2),
),
);
}
return Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: mylist,
);
}
#override
Widget build(BuildContext context) {
print("Is expanded");
return Card(
child: InkWell(
onTap: () {
print("expanded is $expanded");
setState(() {
expanded = !expanded;
});
},
child: ListTile(
title: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: [
Text(
'${widget.records[widget.position].dateLong()} ${widget.records[widget.position].time}'),
Text('Checkin #${records[widget.position].checkinno}'),
],
),
subtitle: !expanded
? Text(
records[position].clinicalRecord.diagnosis_as_string(),
textAlign: TextAlign.left,
style: TextStyle(
// color: Colors.white,
),
)
: Container(
// color: Colors.pink,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: [
Padding(padding: EdgeInsets.symmetric(vertical: 3)),
Text(
records[position].clinicalRecord.diagnosis_as_string(),
textAlign: TextAlign.left,
style: TextStyle(
color: Colors.black,
decorationThickness: 10,
),
),
Padding(padding: EdgeInsets.symmetric(vertical: 3)),
Text(records[position].clinicalRecord.history),
Padding(padding: EdgeInsets.symmetric(vertical: 3)),
Text(records[position].clinicalRecord.examination),
Padding(padding: EdgeInsets.symmetric(vertical: 3)),
Text("Treatment:"),
medicines(records[position].prescribedDrugs),
],
),
),
),
),
);
}
}