Improve check for nested writes

rest_framework/serializers.py

@@ -611,6 +611,7 @@ def raise_errors_on_nested_writes(method_name, serializer, validated_data):
     #     profile = ProfileSerializer()
     assert not any(
         isinstance(field, BaseSerializer) and (key in validated_data)
+        and isinstance(validated_data[key], (list, dict))
         for key, field in serializer.fields.items()
     ), (
         'The `.{method_name}()` method does not support writable nested'
@@ -630,6 +631,7 @@ def raise_errors_on_nested_writes(method_name, serializer, validated_data):
     #     address = serializer.CharField('profile.address')
     assert not any(
         '.' in field.source and (key in validated_data)
+        and isinstance(validated_data[key], (list, dict))
         for key, field in serializer.fields.items()
     ), (
         'The `.{method_name}()` method does not support writable dotted-source '