diff --git a/backend/api/serializers/checks_serializer.py b/backend/api/serializers/checks_serializer.py
index eeafcf17..1ff44824 100644
--- a/backend/api/serializers/checks_serializer.py
+++ b/backend/api/serializers/checks_serializer.py
@@ -7,9 +7,14 @@
 
 
 class FileExtensionSerializer(serializers.ModelSerializer):
+    extension = serializers.CharField(
+        required=True,
+        max_length=10
+    )
+
     class Meta:
         model = FileExtension
-        fields = ["extension"]
+        fields = ["id", "extension"]
 
 
 class StructureCheckSerializer(serializers.ModelSerializer):
@@ -33,24 +38,41 @@ def validate(self, attrs):
         """Validate the structure check"""
         project: Project = self.context["project"]
 
+        # The structure check path should not exist already
         if project.structure_checks.filter(path=attrs["path"]).exists():
             raise ValidationError(_("project.error.structure_checks.already_existing"))
 
+        # The same extension should not be in both blocked and obligated
+        blocked = set([ext["extension"] for ext in attrs["blocked_extensions"]])
+        obligated = set([ext["extension"] for ext in attrs["obligated_extensions"]])
+
+        if blocked.intersection(obligated):
+            raise ValidationError(_("project.error.structure_checks.blocked_obligated"))
+
         return attrs
 
-    def create(self, validated_data):
+    def create(self, validated_data: dict) -> StructureCheck:
         """Create a new structure check"""
         blocked = validated_data.pop("blocked_extensions")
         obligated = validated_data.pop("obligated_extensions")
-        check: StructureCheck = StructureCheck.objects.create(**validated_data)
+
+        check: StructureCheck = StructureCheck.objects.create(
+            path=validated_data.pop("path"),
+            **validated_data
+        )
 
         for ext in obligated:
-            check.obligated_extensions.create(**ext)
+            ext, _ = FileExtension.objects.get_or_create(
+                extension=ext["extension"]
+            )
+            check.obligated_extensions.add(ext)
 
         # Add blocked extensions
-
         for ext in blocked:
-            check.blocked_extensions.create(**ext)
+            ext, _ = FileExtension.objects.get_or_create(
+                extension=ext["extension"]
+            )
+            check.blocked_extensions.add(ext)
 
         return check
 
diff --git a/backend/api/views/project_view.py b/backend/api/views/project_view.py
index f13fedde..4d01e5e4 100644
--- a/backend/api/views/project_view.py
+++ b/backend/api/views/project_view.py
@@ -1,5 +1,6 @@
 import logging
 
+from rest_framework.exceptions import ValidationError
 from rest_framework.parsers import MultiPartParser
 
 from api.models.group import Group
diff --git a/frontend/src/components/forms/ErrorMessage.vue b/frontend/src/components/forms/ErrorMessage.vue
index c6c0e487..b6af146d 100644
--- a/frontend/src/components/forms/ErrorMessage.vue
+++ b/frontend/src/components/forms/ErrorMessage.vue
@@ -3,7 +3,6 @@ import Message from 'primevue/message';
 
 /* Props */
 defineProps<{ field: any }>();
-
 </script>
 
 <template>
diff --git a/frontend/src/components/projects/ProjectForm.vue b/frontend/src/components/projects/ProjectForm.vue
index 6264a025..50be3a9f 100644
--- a/frontend/src/components/projects/ProjectForm.vue
+++ b/frontend/src/components/projects/ProjectForm.vue
@@ -47,7 +47,7 @@ const rules = computed(() => {
 });
 
 const v$ = useVuelidate(rules, form, {
-    $scope: 'form'
+    $scope: 'form',
 });
 
 /**
@@ -119,7 +119,7 @@ watchEffect(() => {
                 <div class="grid">
                     <!-- Start date of the project -->
                     <div class="field col">
-                        <label for="projectStartDate">{{ t('views.projects.start_date') }}</label>
+                        <label for="projectStartDate">{{ t('views.projects.startDate') }}</label>
                         <Calendar
                             id="projectStartDate"
                             class="w-full"
@@ -152,7 +152,7 @@ watchEffect(() => {
                     <!-- Group size for the project -->
                     <div class="field col">
                         <label for="groupSize">
-                            {{ t('views.projects.group_size') }}
+                            {{ t('views.projects.groupSize') }}
                         </label>
                         <InputNumber input-id="groupSize" class="w-full" v-model="form.group_size" :min="1" />
                         <ErrorMessage :field="v$.group_size" />
@@ -160,7 +160,7 @@ watchEffect(() => {
 
                     <!-- Max score for the project -->
                     <div class="field col">
-                        <label for="maxScore">{{ t('views.projects.max_score') }}</label>
+                        <label for="maxScore">{{ t('views.projects.maxScore') }}</label>
                         <InputNumber
                             input-id="maxScore"
                             class="w-full"
diff --git a/frontend/src/components/projects/ProjectStructureTree.vue b/frontend/src/components/projects/ProjectStructureTree.vue
index f840a853..e1f9ca5c 100644
--- a/frontend/src/components/projects/ProjectStructureTree.vue
+++ b/frontend/src/components/projects/ProjectStructureTree.vue
@@ -64,8 +64,8 @@ function deleteStructureCheck(check: StructureCheck): void {
  */
 function updateStructureCheckName(input: HTMLInputElement): void {
     if (editingStructureCheck.value !== null && structureChecks.value !== undefined) {
-        const editing = editingStructureCheck.value;
-        const oldPath = editing.path;
+        const editing: StructureCheck = editingStructureCheck.value;
+        const oldPath: string = editing.path;
 
         editing.setLastFolderName(input.value);
 
@@ -196,6 +196,7 @@ function newTreeNode(check: StructureCheck, key: string, label: string, leaf: bo
                             <InputText
                                 :model-value="node.label"
                                 @change="updateStructureCheckName($event.target as HTMLInputElement)"
+                                @keydown.enter="updateStructureCheckName($event.target as HTMLInputElement)"
                             >
                             </InputText>
                         </template>
diff --git a/frontend/src/test/unit/services/project_service.test.ts b/frontend/src/test/unit/services/project_service.test.ts
index 7dd17ce5..a39fe9f2 100644
--- a/frontend/src/test/unit/services/project_service.test.ts
+++ b/frontend/src/test/unit/services/project_service.test.ts
@@ -1,5 +1,5 @@
 /* eslint-disable @typescript-eslint/no-unused-vars */
-import { describe, it, expect } from 'vitest';
+import { describe, it } from 'vitest';
 
 describe('placeholder', (): void => {
     it('aaaaaaaa', () => {});
diff --git a/frontend/src/test/unit/types/structureCheck.test.ts b/frontend/src/test/unit/types/structureCheck.test.ts
index 7f41fde0..f423a590 100644
--- a/frontend/src/test/unit/types/structureCheck.test.ts
+++ b/frontend/src/test/unit/types/structureCheck.test.ts
@@ -5,7 +5,7 @@ import { describe, it } from 'vitest';
 // import { createStructureCheck } from './helper';
 
 describe('structureCheck type', () => {
-    it('aaaa')
+    it('aaaa');
     // it('create instance of structureCheck with correct properties', () => {
     //     const structureCheck = createStructureCheck(structureCheckData);
     //
diff --git a/frontend/src/types/ApiResponse.ts b/frontend/src/types/ApiResponse.ts
new file mode 100644
index 00000000..c8d0ec66
--- /dev/null
+++ b/frontend/src/types/ApiResponse.ts
@@ -0,0 +1 @@
+export type HyperlinkedRelation = string;
\ No newline at end of file
diff --git a/frontend/src/types/Course.ts b/frontend/src/types/Course.ts
index 6f9b3ca8..fa7d79e4 100644
--- a/frontend/src/types/Course.ts
+++ b/frontend/src/types/Course.ts
@@ -9,17 +9,17 @@ export class Course {
         public id: string = '',
         public name: string = '',
         public excerpt: string = '',
-        public description: string | null = '',
+        public description: string = '',
         public academic_startyear: number = getAcademicYear(),
         public private_course: boolean = false,
-        public invitation_link: string | null = null,
-        public invitation_link_expires: Date | null = null,
+        public invitation_link: string = '',
+        public invitation_link_expires: Date = new Date(),
         public parent_course: Course | null = null,
-        public faculty: Faculty | null = null,
-        public teachers: Teacher[] | null = null,
-        public assistants: Assistant[] | null = null,
-        public students: Student[] | null = null,
-        public projects: Project[] | null = null,
+        public faculty: Faculty = new Faculty(),
+        public teachers: Teacher[] = [],
+        public assistants: Assistant[] = [],
+        public students: Student[] = [],
+        public projects: Project[] = [],
     ) {}
 
     /**
@@ -63,9 +63,6 @@ export class Course {
      * @param course
      */
     static fromJSON(course: Course): Course {
-        const faculty =
-            course.faculty !== undefined && course.faculty !== null ? Faculty.fromJSON(course.faculty) : null;
-
         return new Course(
             course.id,
             course.name,
@@ -76,7 +73,7 @@ export class Course {
             course.invitation_link,
             course.invitation_link_expires,
             course.parent_course,
-            faculty,
+            course.faculty,
         );
     }
 }
diff --git a/frontend/src/types/Faculty.ts b/frontend/src/types/Faculty.ts
index b4d78e08..db503bed 100644
--- a/frontend/src/types/Faculty.ts
+++ b/frontend/src/types/Faculty.ts
@@ -1,7 +1,7 @@
 export class Faculty {
     constructor(
-        public id: string,
-        public name: string,
+        public id: string = '',
+        public name: string = '',
     ) {}
 
     /**
diff --git a/frontend/src/types/FileExtension.ts b/frontend/src/types/FileExtension.ts
index c5e9f985..94117bf0 100644
--- a/frontend/src/types/FileExtension.ts
+++ b/frontend/src/types/FileExtension.ts
@@ -1,5 +1,8 @@
 export class FileExtension {
-    constructor(public extension: string) {}
+    constructor(
+        public id: string = '',
+        public extension: string = '',
+    ) {}
 
     /**
      * Convert a file extension object to a file extension instance.
@@ -7,6 +10,6 @@ export class FileExtension {
      * @param extension
      */
     static fromJSON(extension: FileExtension): FileExtension {
-        return new FileExtension(extension.extension);
+        return new FileExtension(extension.id, extension.extension);
     }
 }
diff --git a/frontend/src/types/StructureCheck.ts b/frontend/src/types/StructureCheck.ts
index 334a690e..bfa32933 100644
--- a/frontend/src/types/StructureCheck.ts
+++ b/frontend/src/types/StructureCheck.ts
@@ -1,5 +1,5 @@
 import { FileExtension } from './FileExtension.ts';
-import { type Project } from './Project.ts';
+import { Project } from './Project.ts';
 
 export class StructureCheck {
     constructor(
@@ -7,7 +7,7 @@ export class StructureCheck {
         public path: string = '',
         public obligated_extensions: FileExtension[] = [],
         public blocked_extensions: FileExtension[] = [],
-        public project: Project | null = null,
+        public project: Project = new Project(),
     ) {}
 
     /**
@@ -51,7 +51,7 @@ export class StructureCheck {
      * @param extensions
      */
     public setBlockedExtensionList(extensions: string[]): void {
-        this.blocked_extensions = extensions.map((extension) => new FileExtension(extension));
+        this.blocked_extensions = extensions.map((extension) => new FileExtension('', extension));
     }
 
     /**
@@ -60,7 +60,7 @@ export class StructureCheck {
      * @param extensions
      */
     public setObligatedExtensionList(extensions: string[]): void {
-        this.obligated_extensions = extensions.map((extension) => new FileExtension(extension));
+        this.obligated_extensions = extensions.map((extension) => new FileExtension('', extension));
     }
 
     /**
@@ -103,6 +103,11 @@ export class StructureCheck {
      * @param structureCheck
      */
     static fromJSON(structureCheck: StructureCheck): StructureCheck {
-        return new StructureCheck(structureCheck.id, structureCheck.path);
+        return new StructureCheck(
+            structureCheck.id,
+            structureCheck.path,
+            structureCheck.obligated_extensions.map(FileExtension.fromJSON),
+            structureCheck.blocked_extensions.map(FileExtension.fromJSON),
+        );
     }
 }
diff --git a/frontend/src/views/projects/UpdateProjectView.vue b/frontend/src/views/projects/UpdateProjectView.vue
index 3926f2ee..7ce381dc 100644
--- a/frontend/src/views/projects/UpdateProjectView.vue
+++ b/frontend/src/views/projects/UpdateProjectView.vue
@@ -53,8 +53,9 @@ async function saveProject(newProject: Project): Promise<void> {
             await setExtraChecks(newProject.extra_checks ?? [], project.value.id);
 
             // Delete the deleted checks
-            const deletedChecks = (project.value.extra_checks ?? []).filter(
-                (check) => !(newProject.extra_checks ?? []).find((newCheck: ExtraCheck) => newCheck.id === check.id),
+            const deletedChecks = project.value.extra_checks.filter(
+                (check) =>
+                    newProject.extra_checks.find((newCheck: ExtraCheck) => newCheck.id === check.id) === undefined,
             );
 
             for (const check of deletedChecks) {