Create a list inside an item of another list - flutter

Question

I have a list of teams to which the logged in user belongs to in my application. Within each team there is a list with the Uids of each team member (teamMembersUid). There is also an empty list in which the information of each user (teamMembers) must be inserted.
Objective: I want to take the Uids of each user in teamMembersUid, extract their information from the database (Firebase firestore) and introduce it into teamMembers list. Here is the team model with the lists:
class TeamModel {
String? uid;
String? teamName;
List<String>? teamMembersUid;
List<UserModel>? teamMembers;
List<String>? publicationsUid;
List<String>? notifications;
List<String>? instancesUid;
TeamModel(
{this.uid,
this.teamName,
this.teamMembersUid,
this.teamMembers,
this.instancesUid,
this.notifications,
this.publicationsUid});
//receiving data from server
factory TeamModel.fromMap(map) {
return TeamModel(
uid: map['uid'],
teamName: map['teamName'],
teamMembersUid: map['teamMembersUid'] is Iterable
? List.from(map['teamMembersUid'])
: null,
teamMembers:
map['teamMembers'] is Iterable ? List.from(map['teamMembers']) : null,
publicationsUid: map['publicationsUid'] is Iterable
? List.from(map['publicationsUid'])
: null,
notifications: map['notifications'] is Iterable
? List.from(map['notifications'])
: null,
instancesUid: map['instancesUid'] is Iterable
? List.from(map['instancesUid'])
: null,
//List.from(['teamMembersUid']), //castFrom adapts teamMembersUid to be a List
);
}
The following function (getTeamsInfoWithUsers) is responsible for:
Create a list with the teams to which the user belongs from firestore.
Extract the Uids of each member of each team.
Get the information from each user from firestore.
Create a list with the information of each user of each team and enter it in teamMembers.
UserModel userData;
List<TeamModel> retVal = [];
try {
//Create a list with the teams to which the user belongs from firestore
final data = await _firestore
.collection("teams")
.where("teamMembersUid", arrayContains: userUid)
.get();
List<TeamModel> data_m =
List.from(data.docs.map((doc) => TeamModel.fromMap(doc)));
//Extract the Uids of each member of each team.
retVal = data_m
.map((team) {
team.teamMembersUid!.map((userUid) async {
//Get the information from each user from firestore.
userData = await getUserInfo(userUid);
//Create a list with the information of each user of each team and enter it in teamMembers.
team.teamMembers!.add(userData);
});
})
.cast<TeamModel>()
.toList();
} catch (e) {
print(e);
}
return retVal;
}```
Problem: The current user belongs to 4 teams and each team has 3 users. Debugging I put a breakpoint in team.teamMembers!.add(userData); line. Since there are 4 teams and each team has 3 users you should see the code stop on that line 12 times, 3 for each team. Instead, it only stops 3 times and doesn't seem to create the list of teamMembers in the data_m variable either. I don't understand why it doesn't work.
Error:
Null error

Answer 1

how about this
retVal = data_m
.map((team) {
team.teamMembersUid!.map((userUid) async {
userData = await getUserInfo(userUid);
team.teamMembers!.add(userData);
}).toList();
})
.cast<TeamModel>()
.toList();
VS