don't crash on empty post with fieldsets

rest/serializers.py

@@ -283,7 +283,6 @@ def get_fields_for_config(self):
         overrides = getattr(self.Meta, "wq_field_config", None) or {}
 
         for name, field in list(fields.items()):
-
             has_wq_config = False
             if name != "id" and not field.read_only and not field.write_only:
                 has_wq_config = True
@@ -567,7 +566,7 @@ def to_virtual_fieldsets(self, data):
         return data
 
     def to_internal_value(self, data):
-        if not getattr(self.Meta, "wq_fieldsets", None):
+        if not data or not getattr(self.Meta, "wq_fieldsets", None):
             return super().to_internal_value(data)
 
         for name, conf in self.Meta.wq_fieldsets.items():

tests/test_post.py

@@ -266,3 +266,12 @@ def test_rest_virtual_fieldset(self):
         self.assertEqual(
             response.data, {"general": {"title": ["This field is required."]}}
         )
+
+    def test_empty_post(self):
+        """
+        Empty post should return 400, not 500
+        """
+        response = self.client.post("/entities.json", data={})
+        self.assertTrue(
+            status.is_client_error(response.status_code), response.data
+        )