Dart/Flutter - the method forEach was called on null - firebase

Question

I'm trying to get the "Child_Name" and "Parent_Name" from firebase rtdb and create a list of the names using ListView.builder. I have done this before in another part of the app and it works perfectly. I am trying to apply the same logic again but I am getting an error.
Error is occurs inside the setState where the line childrenList = Map.from(value) is.
View of my firebase rtdb
is here (image)
Error:
- [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: NoSuchMethodError: The method 'forEach' was called on null.
- Tried calling: forEach(Closure: (dynamic, dynamic) => void)
Code(1):
Future<List> getListOfChildren() async {
print("Getting Children");
databaseReference
.child("users")
.child("Absent_Children")
.child(formattedDate)
.onValue
.listen(
(event) {
setState(
() {
var value = event.snapshot.value;
childrenList = Map.from(value)
.values
.map((e) => Children.fromJson(Map.from(e)))
.toList();
},
);
},
);
return childrenList;
}
Code(2): Class for the data
class Children {
final String childName;
final String parentName;
Children({
this.childName,
this.parentName,
});
static Children fromJson(Map<dynamic, dynamic> json) {
return Children(
childName: json["Child_Name"],
parentName: json["Parent_Name"],
);
}
}
Code(4): formattedDate
getTodaysDate() {
setState(
() {
DateTime now = DateTime.now();
var date = DateFormat("dd-mm-yyyy");
formattedDate = date.format(now).toString();
},
);
}
Code(3): My ListView.builder
body: childrenList.isEmpty
? Center(child: CircularProgressIndicator())
: ListView.builder(
itemCount: childrenList.length,
itemBuilder: (context, int index) {
final Children child = childrenList[index];
final String childName = child.childName;
final String parentName = child.parentName;
return Padding(
padding: const EdgeInsets.all(8.0),
child: Card(
elevation: 0,
child: ExpansionTile(
title: Text(
childName.toUpperCase(),
style: GoogleFonts.lexendMega(),
textAlign: TextAlign.center,
),
children: [
Column(
children: [
Text(
parentName,
textAlign: TextAlign.center,
style: GoogleFonts.lexendMega(fontSize: 13),
),
],
)
],
),
),
);
},
),
Thank you.

Answer 1

As I said here too, it looks like there's no data as databaseReference.child("users").child("Absent_Children").child(formattedDate) and your code doesn't handle that situation.
If the absence of data is a normal occurrence, you should check if the snapshot has a value before trying to access its value:
databaseReference
.child("users")
.child("Absent_Children")
.child(formattedDate)
.onValue
.listen(
(event && event.snapshot.exists) { // 👈 add exists check here
setState(
() {
var value = event.snapshot.value;
childrenList = Map.from(value)
.values
.map((e) => Children.fromJson(Map.from(e)))
.toList();
},
);