diff --git a/lib/group_domain_implementation/lib/src/accessors/firestore_course_member_accessor.dart b/lib/group_domain_implementation/lib/src/accessors/firestore_course_member_accessor.dart
index ac1de887e..a0f066567 100644
--- a/lib/group_domain_implementation/lib/src/accessors/firestore_course_member_accessor.dart
+++ b/lib/group_domain_implementation/lib/src/accessors/firestore_course_member_accessor.dart
@@ -9,9 +9,9 @@
 import 'dart:async';
 import 'dart:developer';
 
+import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:group_domain_models/group_domain_accessors.dart';
 import 'package:group_domain_models/group_domain_models.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:sharezone_common/helper_functions.dart';
 import 'package:sharezone_common/references.dart';
 import 'package:user/user.dart';
@@ -38,10 +38,15 @@ class FirestoreCourseMemberAccessor extends CourseMemberAccessor {
     List<MemberData> membersData = [];
 
     void update() {
-      streamController.add(List.of(membersData)
-        ..addAll(joinedUsersData.where((joinedUser) =>
-                membersData.where((it) => it.id == joinedUser.id).isEmpty) ??
-            []));
+      streamController.add(
+        List.of(membersData)
+          ..addAll(
+            joinedUsersData.where(
+              (joinedUser) =>
+                  membersData.where((it) => it.id == joinedUser.id).isEmpty,
+            ),
+          ),
+      );
     }
 
     final subscription2 = _firestore
@@ -73,8 +78,12 @@ class FirestoreCourseMemberAccessor extends CourseMemberAccessor {
     final subscription = _memberReference(courseID)
         .snapshots()
         .map((snapshot) => snapshot.docs
-            .map((docSnap) =>
-                MemberData.fromData(docSnap.data(), id: docSnap.id))
+            .map(
+              (docSnap) => MemberData.fromData(
+                docSnap.data() as Map<String, dynamic>,
+                id: docSnap.id,
+              ),
+            )
             .toList())
         .listen((newData) {
       membersData = newData;
@@ -92,11 +101,15 @@ class FirestoreCourseMemberAccessor extends CourseMemberAccessor {
   Stream<MemberData> streamSingleMember(String courseID, String memberID) {
     // ignore:close_sinks
     final StreamController<MemberData> streamController = StreamController();
-    MemberData joinedUsersData;
-    MemberData membersData;
+    MemberData? joinedUsersData;
+    MemberData? membersData;
 
     void update() {
-      streamController.add(membersData ?? joinedUsersData);
+      if (membersData != null) {
+        streamController.add(membersData!);
+      } else if (joinedUsersData != null) {
+        streamController.add(joinedUsersData!);
+      }
     }
 
     final subscription2 = _firestore
@@ -110,13 +123,13 @@ class FirestoreCourseMemberAccessor extends CourseMemberAccessor {
         if (docSnapshot.exists) {
           joinedUsersData = MemberData.create(
             id: docSnapshot.id,
-            role: docSnapshot.data()['powerLevel'] == 'owner'
+            role: docSnapshot.data()!['powerLevel'] == 'owner'
                 ? MemberRole.owner
                 : MemberRole.creator,
             user: AppUser.create(id: docSnapshot.id).copyWith(
-                name: docSnapshot.data()['name'],
+                name: docSnapshot.data()!['name'],
                 typeOfUser: enumFromString(
-                    TypeOfUser.values, docSnapshot.data()['typeOfUser'])),
+                    TypeOfUser.values, docSnapshot.data()!['typeOfUser'])),
           );
         } else {
           joinedUsersData = null;
@@ -129,7 +142,9 @@ class FirestoreCourseMemberAccessor extends CourseMemberAccessor {
     final subscription = _memberReference(courseID)
         .doc(memberID)
         .snapshots()
-        .map((docSnap) => MemberData.fromData(docSnap.data(), id: docSnap.id))
+        .map((docSnap) => MemberData.fromData(
+            docSnap.data() as Map<String, dynamic>,
+            id: docSnap.id))
         .listen((newData) {
       membersData = newData;
       update();
diff --git a/lib/group_domain_implementation/lib/src/accessors/firestore_school_class_member_accessor.dart b/lib/group_domain_implementation/lib/src/accessors/firestore_school_class_member_accessor.dart
index 00362aca2..f70a2d8c0 100644
--- a/lib/group_domain_implementation/lib/src/accessors/firestore_school_class_member_accessor.dart
+++ b/lib/group_domain_implementation/lib/src/accessors/firestore_school_class_member_accessor.dart
@@ -6,9 +6,9 @@
 //
 // SPDX-License-Identifier: EUPL-1.2
 
+import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:group_domain_models/group_domain_accessors.dart';
 import 'package:group_domain_models/group_domain_models.dart';
-import 'package:cloud_firestore/cloud_firestore.dart';
 import 'package:sharezone_common/references.dart';
 
 class FirestoreSchoolClassMemberAccessor extends SchoolClassMemberAccessor {
@@ -27,8 +27,10 @@ class FirestoreSchoolClassMemberAccessor extends SchoolClassMemberAccessor {
     return _memberReference(schoolClassID).snapshots().map(
           (snapshot) => snapshot.docs
               .map(
-                (docSnap) =>
-                    MemberData.fromData(docSnap.data(), id: docSnap.id),
+                (docSnap) => MemberData.fromData(
+                  docSnap.data() as Map<String, dynamic>,
+                  id: docSnap.id,
+                ),
               )
               .toList(),
         );
@@ -37,7 +39,10 @@ class FirestoreSchoolClassMemberAccessor extends SchoolClassMemberAccessor {
   @override
   Stream<MemberData> streamSingleMember(String schoolClassID, String memberID) {
     return _memberReference(schoolClassID).doc(memberID).snapshots().map(
-          (snapshot) => MemberData.fromData(snapshot.data(), id: snapshot.id),
+          (snapshot) => MemberData.fromData(
+            snapshot.data() as Map<String, dynamic>,
+            id: snapshot.id,
+          ),
         );
   }
 }
diff --git a/lib/group_domain_implementation/pubspec.yaml b/lib/group_domain_implementation/pubspec.yaml
index e716f0dc6..27a386ac0 100644
--- a/lib/group_domain_implementation/pubspec.yaml
+++ b/lib/group_domain_implementation/pubspec.yaml
@@ -12,7 +12,7 @@ version: 0.0.1
 publish_to: none
 
 environment:
-  sdk: ">=2.10.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   group_domain_models: