Fix bug (exposed by lovasoa#159) in serialization of optional union types (lovasoa#160)

* Fix bug exposed by lovasoa#159 with serialization of optional union types

* Update CHANGELOG.md

* v8.5.2

Author: dairiki

CHANGELOG.md

@@ -1,8 +1,14 @@
 # marshmallow\_dataclass change log
 
+## v8.5.2
+
+- Fix spurious `TypeError` when serializing `Optional` union types with `required=True`
+  ([#160](https://github.com/lovasoa/marshmallow_dataclass/pull/160))
+
 ## v8.5.1
 
- - Allow setting required=True on fields of type Optional (#159)
+- Allow setting required=True on fields of type Optional
+  ([#159](https://github.com/lovasoa/marshmallow_dataclass/pull/159))
 
 ## v8.5.0
 - Fix `default` warning coming from marshmallow. Bump minimal marshmallow version requirement to 3.13. [See #157](https://github.com/lovasoa/marshmallow_dataclass/issues/157).

marshmallow_dataclass/union_field.py

@@ -36,7 +36,7 @@ def _bind_to_schema(self, field_name: str, schema: Schema) -> None:
 
     def _serialize(self, value: Any, attr: str, obj, **kwargs) -> Any:
         errors = []
-        if value is None and not self.required:
+        if value is None:
             return value
         for typ, field in self.union_fields:
             try:

setup.py

@@ -1,6 +1,6 @@
 from setuptools import setup, find_packages
 
-VERSION = "8.5.1"
+VERSION = "8.5.2"
 
 CLASSIFIERS = [
     "Development Status :: 4 - Beta",

tests/test_union.py

@@ -1,3 +1,4 @@
+from dataclasses import field
 import unittest
 from typing import List, Optional, Union, Dict
 
@@ -154,3 +155,14 @@ class Dclass:
 
         for data_in in [{"value": None}, {}]:
             self.assertEqual(schema.dump(schema.load(data_in)), {"value": None})
+
+    def test_required_optional_simple_union(self):
+        @dataclass
+        class Dclass:
+            value: Optional[Union[int, str]] = field(metadata={"required": True})
+
+        schema = Dclass.Schema()
+
+        for value in None, 42, "strvar":
+            self.assertEqual(schema.dump(Dclass(value=value)), {"value": value})
+            self.assertEqual(schema.load({"value": value}), Dclass(value=value))