diff --git a/cvat-ui/.gitignore b/cvat-ui/.gitignore
index 841dae58..4952a5fa 100644
--- a/cvat-ui/.gitignore
+++ b/cvat-ui/.gitignore
@@ -2,4 +2,6 @@
 
 /node_modules
 /dist
+/build
+/yarn.lock
 
diff --git a/cvat/apps/engine/serializers.py b/cvat/apps/engine/serializers.py
index 9ef3556d..08903d7e 100644
--- a/cvat/apps/engine/serializers.py
+++ b/cvat/apps/engine/serializers.py
@@ -26,8 +26,12 @@ class AttributeSerializer(serializers.ModelSerializer):
         return attribute
 
     def to_representation(self, instance):
-        attribute = super().to_representation(instance)
-        attribute['values'] = attribute['values'].split('\n')
+        if instance:
+            attribute = super().to_representation(instance)
+            attribute['values'] = attribute['values'].split('\n')
+        else:
+            attribute = instance
+
         return attribute
 
 class LabelSerializer(serializers.ModelSerializer):
@@ -75,8 +79,11 @@ class ClientFileSerializer(serializers.ModelSerializer):
 
     # pylint: disable=no-self-use
     def to_representation(self, instance):
-        upload_dir = instance.task.get_upload_dirname()
-        return instance.file.path[len(upload_dir) + 1:]
+        if instance:
+            upload_dir = instance.task.get_upload_dirname()
+            return instance.file.path[len(upload_dir) + 1:]
+        else:
+            return instance
 
 class ServerFileSerializer(serializers.ModelSerializer):
     class Meta:
@@ -89,7 +96,7 @@ class ServerFileSerializer(serializers.ModelSerializer):
 
     # pylint: disable=no-self-use
     def to_representation(self, instance):
-        return instance.file
+        return instance.file if instance else instance
 
 class RemoteFileSerializer(serializers.ModelSerializer):
     class Meta:
@@ -102,7 +109,7 @@ class RemoteFileSerializer(serializers.ModelSerializer):
 
     # pylint: disable=no-self-use
     def to_representation(self, instance):
-        return instance.file
+        return instance.file if instance else instance
 
 class RqStatusSerializer(serializers.Serializer):
     state = serializers.ChoiceField(choices=[
diff --git a/cvat/apps/engine/urls.py b/cvat/apps/engine/urls.py
index 6631874b..eef0ab2e 100644
--- a/cvat/apps/engine/urls.py
+++ b/cvat/apps/engine/urls.py
@@ -37,9 +37,12 @@ urlpatterns = [
     path('dashboard/', views.dispatch_request),
 
     # documentation for API
-    path('api/swagger.<slug:format>$', schema_view.without_ui(cache_timeout=0), name='schema-json'),
-    path('api/swagger/', schema_view.with_ui('swagger', cache_timeout=0), name='schema-swagger-ui'),
-    path('api/docs/', schema_view.with_ui('redoc', cache_timeout=0), name='schema-redoc'),
+    path('api/swagger<str:scheme>', views.wrap_swagger(
+       schema_view.without_ui(cache_timeout=0)), name='schema-json'),
+    path('api/swagger/', views.wrap_swagger(
+       schema_view.with_ui('swagger', cache_timeout=0)), name='schema-swagger-ui'),
+    path('api/docs/', views.wrap_swagger(
+       schema_view.with_ui('redoc', cache_timeout=0)), name='schema-redoc'),
 
     # entry point for API
     path('api/v1/auth/', include('cvat.apps.authentication.api_urls')),
diff --git a/cvat/apps/engine/views.py b/cvat/apps/engine/views.py
index b6ad69d6..c4e81647 100644
--- a/cvat/apps/engine/views.py
+++ b/cvat/apps/engine/views.py
@@ -55,6 +55,22 @@ from django.utils.decorators import method_decorator
 from drf_yasg.inspectors import NotHandled, CoreAPICompatInspector
 from django_filters.rest_framework import DjangoFilterBackend
 
+# drf-yasg component doesn't handle correctly URL_FORMAT_OVERRIDE and
+# send requests with ?format=openapi suffix instead of ?scheme=openapi.
+# We map the required paramater explicitly and add it into query arguments
+# on the server side.
+def wrap_swagger(view):
+    @login_required
+    def _map_format_to_schema(request, scheme=None):
+        if 'format' in request.GET:
+            request.GET = request.GET.copy()
+            format_alias = settings.REST_FRAMEWORK['URL_FORMAT_OVERRIDE']
+            request.GET[format_alias] = request.GET['format']
+
+        return view(request, format=scheme)
+
+    return _map_format_to_schema
+
 # Server REST API
 @login_required
 def dispatch_request(request):
diff --git a/cvat/requirements/base.txt b/cvat/requirements/base.txt
index 5fe31b00..7b688b34 100644
--- a/cvat/requirements/base.txt
+++ b/cvat/requirements/base.txt
@@ -30,9 +30,9 @@ GitPython==2.1.11
 coreapi==2.3.3
 django-filter==2.0.0
 Markdown==3.0.1
-djangorestframework==3.9.1
+djangorestframework==3.9.3
 Pygments==2.3.1
-drf-yasg==1.16.0
+drf-yasg==1.17.0
 Shapely==1.6.4.post2
 pdf2image==1.6.0
 pascal_voc_writer==0.1.4
diff --git a/cvat/settings/base.py b/cvat/settings/base.py
index 961c792f..08ae7e2b 100644
--- a/cvat/settings/base.py
+++ b/cvat/settings/base.py
@@ -145,7 +145,7 @@ REST_FRAMEWORK = {
         'rest_framework.filters.OrderingFilter'),
 
     # Disable default handling of the 'format' query parameter by REST framework
-    'URL_FORMAT_OVERRIDE': None,
+    'URL_FORMAT_OVERRIDE': 'scheme',
 }
 
 REST_AUTH_REGISTER_SERIALIZERS = {