Optional allows None

Author: python-desert

src/desert/_make.py

@@ -201,6 +201,7 @@ def field_for_schema(
 
     if default is not marshmallow.missing:
         desert_metadata.setdefault("default", default)
+        desert_metadata.setdefault('allow_none', True)
         if not desert_metadata.get(
             "required"
         ):  # 'missing' must not be set for required fields.
@@ -242,9 +243,11 @@ def field_for_schema(
             metadata[_DESERT_SENTINEL]["missing"] = metadata.get("missing", None)
             metadata[_DESERT_SENTINEL]["required"] = False
 
+
             field = field_for_schema(subtyp, metadata=metadata, default=None)
             field.default = None
             field.missing = None
+            field.allow_none = True
 
         elif typing_inspect.is_union_type(typ):
             subfields = [field_for_schema(subtyp) for subtyp in arguments]

tests/test_make.py

@@ -137,6 +137,16 @@ class A:
     data = desert.schema_class(A)().load({})
     assert data == A(None)
 
+def test_optional_present(module):
+    """Setting an optional type allows passing None."""
+
+    @module.dataclass
+    class A:
+        x: t.Optional[int]
+
+    data = desert.schema_class(A)().load({"x": None})
+    assert data == A(None)
+
 
 def test_custom_field(module):
     @module.dataclass