diff --git a/firka/lib/services/live_activity_service.dart b/firka/lib/services/live_activity_service.dart
index 0b23462..5ddd16e 100644
--- a/firka/lib/services/live_activity_service.dart
+++ b/firka/lib/services/live_activity_service.dart
@@ -1581,12 +1581,12 @@ class LiveActivityService {
       final emptyType = NameUidDesc(
         uid: 'placeholder',
         name: 'Placeholder',
-        description: null,
+        description: '',
       );
       final emptyState = NameUidDesc(
         uid: 'active',
         name: 'Active',
-        description: null,
+        description: '',
       );
 
       placeholderLesson = Lesson(
diff --git a/firka/lib/ui/phone/pages/home/home_grades.dart b/firka/lib/ui/phone/pages/home/home_grades.dart
index 82a3b20..331aa96 100644
--- a/firka/lib/ui/phone/pages/home/home_grades.dart
+++ b/firka/lib/ui/phone/pages/home/home_grades.dart
@@ -156,18 +156,7 @@ class _HomeGradesScreen extends FirkaState<HomeGradesScreen> {
       if (lessons != null && lessons!.response != null) {
         for (var lesson in lessons!.response!) {
           if (subjects.where((s) => s.uid == lesson.uid).isEmpty) {
-            subjects.add(
-              Subject(
-                uid: lesson.uid,
-                name: lesson.name,
-                category: NameUidDesc(
-                  uid: lesson.subjectCategoryId,
-                  name: lesson.subjectCategoryName,
-                  description: lesson.subjectCategoryDescription,
-                ),
-                sortIndex: lesson.sortIndex,
-              ),
-            );
+            subjects.add(lesson.subject);
           }
         }
       }
diff --git a/kreta_api/lib/src/extensions.dart b/kreta_api/lib/src/extensions.dart
new file mode 100644
index 0000000..740bb09
--- /dev/null
+++ b/kreta_api/lib/src/extensions.dart
@@ -0,0 +1,17 @@
+extension JsonHelper on Map<String, dynamic> {
+  double? dbl(String key) {
+    final value = this[key];
+    if (value == null) {
+      return null;
+    }
+    return (value as num).toDouble();
+  }
+
+  DateTime? localDate(String key) {
+    final value = this[key];
+    if (value == null) {
+      return null;
+    }
+    return DateTime.parse(value as String).toLocal();
+  }
+}
diff --git a/kreta_api/lib/src/model/class_group.dart b/kreta_api/lib/src/model/class_group.dart
index d520c58..edfed1f 100644
--- a/kreta_api/lib/src/model/class_group.dart
+++ b/kreta_api/lib/src/model/class_group.dart
@@ -1,4 +1,6 @@
+import '../extensions.dart';
 import 'generic.dart';
+import 'subject.dart';
 
 class ClassGroup {
   final String uid;
@@ -27,17 +29,11 @@ class ClassGroup {
     return ClassGroup(
       uid: json['Uid'],
       name: json['Nev'],
-      headTeacher: json['OsztalyFonok'] != null
-          ? UidObj.fromJson(json['OsztalyFonok'])
-          : null,
-      substituteHeadTeacher: json['OsztalyFonokHelyettes'] != null
-          ? UidObj.fromJson(json['OsztalyFonokHelyettes'])
-          : null,
-      studyGroup: NameUidDesc.fromJson(json['OktatasNevelesiKategoria']),
+      headTeacher: json.uid('OsztalyFonok'),
+      substituteHeadTeacher: json.uid('OsztalyFonokHelyettes'),
+      studyGroup: json.nameUidDesc('OktatasNevelesiKategoria')!,
       studyGroupSortIndex: json['OktatasNevelesiKategoriaSortIndex'],
-      studyTask: json['OktatasNevelesiFeladat'] != null
-          ? NameUidDesc.fromJson(json['OktatasNevelesiFeladat'])
-          : null,
+      studyTask: json.nameUidDesc('OktatasNevelesiFeladat'),
       isActive: json['IsAktiv'],
       type: json['Tipus'],
     );
@@ -59,55 +55,32 @@ class ClassGroup {
   }
 }
 
-class SubjectAverage {
-  final String uid;
-  final String name;
-  final String? teacherName;
-  final String subjectCategoryId;
-  final String subjectCategoryName;
-  final String subjectCategoryDescription;
+class SubjectAverage extends UidObj {
+  final Subject subject;
   final double? average;
   final double? weightedSum;
   final double? weightedCount;
-  final int sortIndex;
 
   SubjectAverage({
-    required this.uid,
-    required this.name,
-    this.teacherName,
-    required this.subjectCategoryId,
-    required this.subjectCategoryName,
-    required this.subjectCategoryDescription,
+    required super.uid,
+    required this.subject,
     this.average,
     this.weightedSum,
     this.weightedCount,
-    required this.sortIndex,
   });
 
   factory SubjectAverage.fromJson(Map<String, dynamic> json) {
-    final tantargy = json['Tantargy'] ?? {};
-    final kategori = tantargy['Kategoria'] ?? {};
-
     return SubjectAverage(
-      uid: json['Uid'] ?? '',
-      name: tantargy['Nev'] ?? '',
-      teacherName: json['TeacherName'],
-      subjectCategoryId: kategori['Uid'] ?? '',
-      subjectCategoryName: kategori['Nev'] ?? '',
-      subjectCategoryDescription: kategori['Leiras'] ?? '',
-      average: json['Atlag'] != null ? (json['Atlag'] as num).toDouble() : null,
-      weightedSum: json['SulyozottOsztalyzatOsszege'] != null
-          ? (json['SulyozottOsztalyzatOsszege'] as num).toDouble()
-          : null,
-      weightedCount: json['SulyozottOsztalyzatSzama'] != null
-          ? (json['SulyozottOsztalyzatSzama'] as num).toDouble()
-          : null,
-      sortIndex: tantargy['SortIndex'] ?? 0,
+      uid: json['Uid'],
+      subject: Subject.fromJson(json['Tantargy']),
+      average: json.dbl('Atlag'),
+      weightedSum: json.dbl('SulyozottOsztalyzatOsszege'),
+      weightedCount: json.dbl('SulyozottOsztalyzatSzama'),
     );
   }
 
   @override
   String toString() {
-    return 'SubjectAverage(uid: "$uid", name: "$name", category: "$subjectCategoryName", average: $average)';
+    return 'SubjectAverage(uid: "$uid", name: "${subject.name}", category: "${subject.category.name}", average: $average)';
   }
 }
diff --git a/kreta_api/lib/src/model/generic.dart b/kreta_api/lib/src/model/generic.dart
index cb2d276..74b0341 100644
--- a/kreta_api/lib/src/model/generic.dart
+++ b/kreta_api/lib/src/model/generic.dart
@@ -1,11 +1,9 @@
-class NameUidDesc {
-  final String uid;
-  final String? name;
-  final String? description;
+class NameUidDesc extends NameUid {
+  final String description;
 
   NameUidDesc({
-    required this.uid,
-    required this.name,
+    required super.uid,
+    required super.name,
     required this.description,
   });
 
@@ -31,11 +29,10 @@ class NameUidDesc {
   }
 }
 
-class NameUid {
-  final String uid;
+class NameUid extends UidObj {
   final String name;
 
-  NameUid({required this.uid, required this.name});
+  NameUid({required super.uid, required this.name});
 
   factory NameUid.fromJson(Map<String, dynamic> json) {
     return NameUid(uid: json['Uid'], name: json['Nev']);
@@ -62,3 +59,29 @@ class UidObj {
         ')';
   }
 }
+
+extension ToUidObj on Map<String, dynamic> {
+  UidObj? uid(String key) {
+    final value = this[key];
+    if (value == null) {
+      return null;
+    }
+    return UidObj.fromJson(value);
+  }
+
+  NameUid? nameUid(String key) {
+    final value = this[key];
+    if (value == null) {
+      return null;
+    }
+    return NameUid.fromJson(value);
+  }
+
+  NameUidDesc? nameUidDesc(String key) {
+    final value = this[key];
+    if (value == null) {
+      return null;
+    }
+    return NameUidDesc.fromJson(value);
+  }
+}
diff --git a/kreta_api/lib/src/model/grade.dart b/kreta_api/lib/src/model/grade.dart
index ef04aaa..7a7e00d 100644
--- a/kreta_api/lib/src/model/grade.dart
+++ b/kreta_api/lib/src/model/grade.dart
@@ -1,8 +1,7 @@
 import 'generic.dart';
 import 'subject.dart';
 
-class Grade {
-  final String uid;
+class Grade extends UidObj {
   final DateTime recordDate;
   final DateTime creationDate;
   final DateTime? ackDate;
@@ -21,7 +20,7 @@ class Grade {
   final int sortIndex;
 
   Grade({
-    required this.uid,
+    required super.uid,
     required this.recordDate,
     required this.creationDate,
     this.ackDate,
@@ -50,18 +49,16 @@ class Grade {
           : null,
       subject: Subject.fromJson(json['Tantargy']),
       topic: json['Tema'],
-      type: NameUidDesc.fromJson(json['Tipus']),
-      mode: json['Mod'] != null ? NameUidDesc.fromJson(json['Mod']) : null,
-      valueType: NameUidDesc.fromJson(json['ErtekFajta']),
+      type: json.nameUidDesc('Tipus')!,
+      mode: json.nameUidDesc('Mod'),
+      valueType: json.nameUidDesc('ErtekFajta')!,
       teacher: json['ErtekeloTanarNeve'],
       kind: json['Kind'],
       numericValue: json['SzamErtek'],
       strValue: json['SzovegesErtek'],
       weightPercentage: json['SulySzazalekErteke'],
       shortStrValue: json['SzovegesErtekelesRovidNev'],
-      classGroup: json['OsztalyCsoport'] != null
-          ? UidObj.fromJson(json['OsztalyCsoport'])
-          : null,
+      classGroup: json.uid('OsztalyCsoport'),
       sortIndex: json['SortIndex'],
     );
   }
diff --git a/kreta_api/lib/src/model/guardian.dart b/kreta_api/lib/src/model/guardian.dart
index 123bf4f..22ce4f3 100644
--- a/kreta_api/lib/src/model/guardian.dart
+++ b/kreta_api/lib/src/model/guardian.dart
@@ -1,16 +1,16 @@
-class Guardian {
+import 'generic.dart';
+
+class Guardian extends NameUid {
   final String? email;
   final bool isLegalRepresentative;
-  final String? name;
   final String? phoneNumber;
-  final String uid;
 
   Guardian({
     required this.email,
     required this.isLegalRepresentative,
-    required this.name,
+    required super.name,
     required this.phoneNumber,
-    required this.uid,
+    required super.uid,
   });
 
   factory Guardian.fromJson(Map<String, dynamic> json) {
diff --git a/kreta_api/lib/src/model/homework.dart b/kreta_api/lib/src/model/homework.dart
index d3662a7..34c1324 100644
--- a/kreta_api/lib/src/model/homework.dart
+++ b/kreta_api/lib/src/model/homework.dart
@@ -1,8 +1,8 @@
+import '../extensions.dart';
 import 'generic.dart';
 import 'subject.dart';
 
-class Homework {
-  final String uid;
+class Homework extends UidObj {
   final Subject subject;
   final String subjectName;
   final String teacherName;
@@ -17,7 +17,7 @@ class Homework {
   final bool canAttach;
 
   Homework({
-    required this.uid,
+    required super.uid,
     required this.subject,
     required this.subjectName,
     required this.teacherName,
@@ -39,13 +39,13 @@ class Homework {
       subjectName: json["TantargyNeve"],
       teacherName: json["RogzitoTanarNeve"],
       description: json["Szoveg"],
-      startDate: DateTime.parse(json["FeladasDatuma"]).toLocal(),
-      dueDate: DateTime.parse(json["HataridoDatuma"]).toLocal(),
-      creationDate: DateTime.parse(json["RogzitesIdopontja"]).toLocal(),
+      startDate: json.localDate("FeladasDatuma")!,
+      dueDate: json.localDate("HataridoDatuma")!,
+      creationDate: json.localDate("RogzitesIdopontja")!,
       isCreatedByTeacher: json["IsTanarRogzitette"],
       isDone: json["IsMegoldva"],
       canBeSubmitted: json["IsBeadhato"],
-      classGroup: UidObj.fromJson(json["OsztalyCsoport"]),
+      classGroup: json.uid("OsztalyCsoport")!,
       canAttach: json["IsCsatolasEngedelyezes"],
     );
   }
diff --git a/kreta_api/lib/src/model/institution.dart b/kreta_api/lib/src/model/institution.dart
index 5424854..0900d94 100644
--- a/kreta_api/lib/src/model/institution.dart
+++ b/kreta_api/lib/src/model/institution.dart
@@ -1,14 +1,15 @@
-class Institution {
+import 'generic.dart';
+
+class Institution extends UidObj {
   final CustomizationSettings customizationSettings;
   final String shortName;
   final List<SystemModule> systemModuleList;
-  final String uid;
 
   Institution({
     required this.customizationSettings,
     required this.shortName,
     required this.systemModuleList,
-    required this.uid,
+    required super.uid,
   });
 
   factory Institution.fromJson(Map<String, dynamic> json) {
diff --git a/kreta_api/lib/src/model/notice_board.dart b/kreta_api/lib/src/model/notice_board.dart
index 52d9cc2..0fae62a 100644
--- a/kreta_api/lib/src/model/notice_board.dart
+++ b/kreta_api/lib/src/model/notice_board.dart
@@ -1,7 +1,7 @@
+import '../extensions.dart';
 import 'generic.dart';
 
-class NoticeBoardItem {
-  final String uid;
+class NoticeBoardItem extends UidObj {
   final String author;
   final DateTime validFrom;
   final DateTime validTo;
@@ -10,7 +10,7 @@ class NoticeBoardItem {
   final String contentText;
 
   NoticeBoardItem({
-    required this.uid,
+    required super.uid,
     required this.author,
     required this.validFrom,
     required this.validTo,
@@ -23,8 +23,8 @@ class NoticeBoardItem {
     return NoticeBoardItem(
       uid: json['Uid'],
       author: json['RogzitoNeve'],
-      validFrom: DateTime.parse(json['ErvenyessegKezdete']),
-      validTo: DateTime.parse(json['ErvenyessegVege']),
+      validFrom: json.localDate('ErvenyessegKezdete')!,
+      validTo: json.localDate('ErvenyessegVege')!,
       title: json['Cim'],
       contentHTML: json['Tartalom'],
       contentText: json['TartalomText'],
@@ -45,8 +45,7 @@ class NoticeBoardItem {
   }
 }
 
-class InfoBoardItem {
-  final String uid;
+class InfoBoardItem extends UidObj {
   final String title;
   final DateTime date;
   final String author;
@@ -56,7 +55,7 @@ class InfoBoardItem {
   final NameUidDesc type;
 
   InfoBoardItem({
-    required this.uid,
+    required super.uid,
     required this.title,
     required this.date,
     required this.author,
@@ -70,12 +69,12 @@ class InfoBoardItem {
     return InfoBoardItem(
       uid: json['Uid'],
       title: json['Cim'],
-      date: DateTime.parse(json['Datum']),
+      date: json.localDate('Datum')!,
       author: json['KeszitoTanarNeve'],
-      createdAt: DateTime.parse(json['KeszitesDatuma']),
+      createdAt: json.localDate('KeszitesDatuma')!,
       contentText: json['Tartalom'],
       contentHTML: json['TartalomFormazott'],
-      type: NameUidDesc.fromJson(json['Tipus']),
+      type: json.nameUidDesc('Tipus')!,
     );
   }
 
diff --git a/kreta_api/lib/src/model/omission.dart b/kreta_api/lib/src/model/omission.dart
index 9c354bc..b3ac732 100644
--- a/kreta_api/lib/src/model/omission.dart
+++ b/kreta_api/lib/src/model/omission.dart
@@ -1,8 +1,8 @@
+import '../extensions.dart';
 import 'generic.dart';
 import 'subject.dart';
 
-class Omission {
-  final String uid;
+class Omission extends UidObj {
   final Subject subject;
   final Class? c;
   final DateTime date;
@@ -16,7 +16,7 @@ class Omission {
   final UidObj? classGroup;
 
   Omission({
-    required this.uid,
+    required super.uid,
     required this.subject,
     required this.c,
     required this.date,
@@ -35,19 +35,15 @@ class Omission {
       uid: json['Uid'],
       subject: Subject.fromJson(json['Tantargy']),
       c: json['Osztaly'] != null ? Class.fromJson(json['Osztaly']) : null,
-      date: DateTime.parse(json['Datum']).toLocal(),
+      date: json.localDate('Datum')!,
       teacher: json['RogzitoTanarNeve'],
-      type: json['Tipus'] != null ? NameUidDesc.fromJson(json['Tipus']) : null,
-      mode: json['Mod'] != null ? NameUidDesc.fromJson(json['Mod']) : null,
+      type: json.nameUidDesc('Tipus'),
+      mode: json.nameUidDesc('Mod'),
       lateForMin: json['KesesPercben'],
-      createdAt: DateTime.parse(json['KeszitesDatuma']).toLocal(),
+      createdAt: json.localDate('KeszitesDatuma')!,
       state: json['IgazolasAllapota'],
-      proofType: json['IgazolasTipusa'] != null
-          ? NameUidDesc.fromJson(json['IgazolasTipusa'])
-          : null,
-      classGroup: json['OsztalyCsoport'] != null
-          ? UidObj.fromJson(json['OsztalyCsoport'])
-          : null,
+      proofType: json.nameUidDesc('IgazolasTipusa'),
+      classGroup: json.uid('OsztalyCsoport'),
     );
   }
 
@@ -79,8 +75,8 @@ class Class {
 
   factory Class.fromJson(Map<String, dynamic> json) {
     return Class(
-      start: DateTime.parse(json['KezdoDatum']).toLocal(),
-      end: DateTime.parse(json['VegDatum']).toLocal(),
+      start: json.localDate('KezdoDatum')!,
+      end: json.localDate('VegDatum')!,
       classNo: json['Oraszam'],
     );
   }
diff --git a/kreta_api/lib/src/model/subject.dart b/kreta_api/lib/src/model/subject.dart
index 25060b4..dea12b9 100644
--- a/kreta_api/lib/src/model/subject.dart
+++ b/kreta_api/lib/src/model/subject.dart
@@ -1,15 +1,13 @@
 import 'generic.dart';
 
-class Subject {
-  final String uid;
-  final String name;
+class Subject extends NameUid {
   final NameUidDesc category;
   final int sortIndex;
   final String? teacherName;
 
   Subject({
-    required this.uid,
-    required this.name,
+    required super.uid,
+    required super.name,
     required this.category,
     required this.sortIndex,
     this.teacherName,
@@ -19,7 +17,7 @@ class Subject {
     return Subject(
       uid: json['Uid'],
       name: json['Nev'],
-      category: NameUidDesc.fromJson(json['Kategoria']),
+      category: json.nameUidDesc('Kategoria')!,
       sortIndex: json['SortIndex'],
       teacherName: json['alkalmazottNev'],
     );
diff --git a/kreta_api/lib/src/model/test.dart b/kreta_api/lib/src/model/test.dart
index 9e685a5..f8319a4 100644
--- a/kreta_api/lib/src/model/test.dart
+++ b/kreta_api/lib/src/model/test.dart
@@ -1,8 +1,8 @@
+import '../extensions.dart';
 import 'generic.dart';
 import 'subject.dart';
 
-class Test {
-  final String uid;
+class Test extends UidObj {
   final DateTime date;
   final DateTime reportDate;
   final String teacherName;
@@ -14,7 +14,7 @@ class Test {
   final UidObj classGroup;
 
   Test({
-    required this.uid,
+    required super.uid,
     required this.date,
     required this.reportDate,
     required this.teacherName,
@@ -29,15 +29,15 @@ class Test {
   factory Test.fromJson(Map<String, dynamic> json) {
     return Test(
       uid: json['Uid'],
-      date: DateTime.parse(json['Datum']).toLocal(),
-      reportDate: DateTime.parse(json['BejelentesDatuma']).toLocal(),
+      date: json.localDate('Datum')!,
+      reportDate: json.localDate('BejelentesDatuma')!,
       teacherName: json['RogzitoTanarNeve'],
       lessonNumber: json['OrarendiOraOraszama'],
       subject: Subject.fromJson(json['Tantargy']),
       subjectName: json['TantargyNeve'],
       theme: json['Temaja'],
-      method: NameUidDesc.fromJson(json['Modja']),
-      classGroup: UidObj.fromJson(json['OsztalyCsoport']),
+      method: json.nameUidDesc('Modja')!,
+      classGroup: json.uid('OsztalyCsoport')!,
     );
   }
 
diff --git a/kreta_api/lib/src/model/timetable.dart b/kreta_api/lib/src/model/timetable.dart
index 8fb5efc..6d4debe 100644
--- a/kreta_api/lib/src/model/timetable.dart
+++ b/kreta_api/lib/src/model/timetable.dart
@@ -1,12 +1,11 @@
+import '../extensions.dart';
 import 'generic.dart';
 import 'subject.dart';
 
-class Lesson {
-  final String uid;
+class Lesson extends NameUid {
   final String date;
   final DateTime start;
   final DateTime end;
-  final String name;
   final int? lessonNumber;
   final int? lessonSeqNumber;
   final NameUid? classGroup;
@@ -33,11 +32,11 @@ class Lesson {
   final DateTime lastModifiedAt;
 
   Lesson({
-    required this.uid,
+    required super.uid,
     required this.date,
     required this.start,
     required this.end,
-    required this.name,
+    required super.name,
     this.lessonNumber,
     this.lessonSeqNumber,
     this.classGroup,
@@ -74,25 +73,21 @@ class Lesson {
     return Lesson(
       uid: json['Uid'],
       date: json['Datum'],
-      start: DateTime.parse(json['KezdetIdopont']).toLocal(),
-      end: DateTime.parse(json['VegIdopont']).toLocal(),
+      start: json.localDate('KezdetIdopont')!,
+      end: json.localDate('VegIdopont')!,
       name: json['Nev'],
       lessonNumber: json['Oraszam'],
       lessonSeqNumber: json['OraEvesSorszama'],
-      classGroup: json['OsztalyCsoport'] != null
-          ? NameUid.fromJson(json['OsztalyCsoport'])
-          : null,
+      classGroup: json.nameUid('OsztalyCsoport'),
       teacher: json['TanarNeve'],
       subject: json['Tantargy'] != null
           ? Subject.fromJson(json['Tantargy'])
           : null,
       theme: json['Tema'],
       roomName: json['TeremNeve'],
-      type: NameUidDesc.fromJson(json['Tipus']),
-      studentPresence: json['TanuloJelenlet'] != null
-          ? NameUidDesc.fromJson(json['TanuloJelenlet'])
-          : null,
-      state: NameUidDesc.fromJson(json['Allapot']),
+      type: json.nameUidDesc('Tipus')!,
+      studentPresence: json.nameUidDesc('TanuloJelenlet'),
+      state: json.nameUidDesc('Allapot')!,
       substituteTeacher: json['HelyettesTanarNeve'],
       homeworkUid: json['HaziFeladatUid'],
       taskGroupUid: json['FeladatGroupUid'],
@@ -108,8 +103,8 @@ class Lesson {
           json['DigitalisTamogatoEszkozTipusList'] != null
           ? List<String>.from(json['DigitalisTamogatoEszkozTipusList'])
           : List<String>.empty(),
-      createdAt: DateTime.parse(json['Letrehozas']).toLocal(),
-      lastModifiedAt: DateTime.parse(json['UtolsoModositas']).toLocal(),
+      createdAt: json.localDate('Letrehozas')!,
+      lastModifiedAt: json.localDate('UtolsoModositas')!,
     );
   }