Do not treat missing non-form data as empty dict

This allows views to distinguish missing payload from empty payload.

Related: #3647, #4566

docs/api-guide/requests.md

@@ -24,6 +24,7 @@ REST framework's Request objects provide flexible request parsing that allows yo
 * It includes all parsed content, including *file and non-file* inputs.
 * It supports parsing the content of HTTP methods other than `POST`, meaning that you can access the content of `PUT` and `PATCH` requests.
 * It supports REST framework's flexible request parsing, rather than just supporting form data.  For example you can handle incoming [JSON data] similarly to how you handle incoming [form data].
+* If the client does not send any data and does not specify form encoding, the value of `.data` is determined by the `DEFAULT_MISSING_DATA` setting. If form encoding is used and no data is sent, `.data` will be an empty Django `QueryDict`.
 
 For more details see the [parsers documentation].
 

docs/api-guide/settings.md

@@ -103,6 +103,13 @@ A view inspector class that will be used for schema generation.
 
 Default: `'rest_framework.schemas.openapi.AutoSchema'`
 
+#### DEFAULT_MISSING_DATA
+
+The value that should be used for `request.data` when the client did not send any data in the request body. This
+setting applies only if the client did not send a header indicating form encoding.
+
+Default: `None`
+
 ---
 
 ## Generic view settings

rest_framework/request.py

@@ -341,7 +341,7 @@ class Request:
             if media_type and is_form_media_type(media_type):
                 empty_data = QueryDict('', encoding=self._request._encoding)
             else:
-                empty_data = {}
+                empty_data = api_settings.DEFAULT_MISSING_DATA
             empty_files = MultiValueDict()
             return (empty_data, empty_files)
 

rest_framework/settings.py

@@ -46,6 +46,7 @@ DEFAULTS = {
     'DEFAULT_CONTENT_NEGOTIATION_CLASS': 'rest_framework.negotiation.DefaultContentNegotiation',
     'DEFAULT_METADATA_CLASS': 'rest_framework.metadata.SimpleMetadata',
     'DEFAULT_VERSIONING_CLASS': None,
+    'DEFAULT_MISSING_DATA': None,
 
     # Generic view behavior
     'DEFAULT_PAGINATION_CLASS': None,

tests/test_request.py

@@ -56,14 +56,14 @@ class TestContentParsing(TestCase):
         Ensure request.data returns empty QueryDict for GET request.
         """
         request = Request(factory.get('/'))
-        assert request.data == {}
+        assert request.data is None
 
     def test_standard_behaviour_determines_no_content_HEAD(self):
         """
         Ensure request.data returns empty QueryDict for HEAD request.
         """
         request = Request(factory.head('/'))
-        assert request.data == {}
+        assert request.data is None
 
     def test_request_DATA_with_form_content(self):
         """

tests/test_testing.py

@@ -42,6 +42,7 @@ class BasicSerializer(serializers.Serializer):
 @api_view(['POST'])
 def post_view(request):
     serializer = BasicSerializer(data=request.data)
+    serializer.allow_null = ('allow_null' in request.query_params)
     serializer.is_valid(raise_exception=True)
     return Response(serializer.validated_data)
 
@@ -191,7 +192,26 @@ class TestAPITestClient(TestCase):
             path='/view/', data={'valid': 123, 'invalid': {'a': 123}}
         )
 
-    def test_empty_post_uses_default_boolean_value(self):
+    def test_missing_post_payload_causes_400(self):
+        response = self.client.post(
+            '/post-view/',
+            data=None,
+            content_type='application/json'
+        )
+        assert response.status_code == 400
+        assert response.data['non_field_errors'] == ['No data provided']
+
+    def test_missing_post_payload_allow_null_causes_200(self):
+        response = self.client.post(
+            '/post-view/?allow_null=1',
+            data=None,
+            content_type='application/json'
+        )
+        assert response.status_code == 200
+        assert response.data is None
+
+    @override_settings(REST_FRAMEWORK={'DEFAULT_MISSING_DATA': {}})
+    def test_missing_post_payload_coerced_dict_uses_default_boolean_value(self):
         response = self.client.post(
             '/post-view/',
             data=None,