fix: handle Optional type recursive models (#584)

polyfactory/factories/base.py

@@ -716,8 +716,10 @@ def get_field_value(  # noqa: C901, PLR0911, PLR0912
 
             # `None` is removed from the children when creating FieldMeta so when `children`
             # is empty, it must mean that the field meta is an optional type.
-            if children:
-                return cls.get_field_value(cls.__random__.choice(children), field_build_parameters, build_context)
+            if not children:
+                return None
+
+            return cls.get_field_value(cls.__random__.choice(children), field_build_parameters, build_context)
 
         if BaseFactory.is_factory_type(annotation=unwrapped_annotation):
             if not field_build_parameters and unwrapped_annotation in build_context["seen_models"]:

tests/test_recursive_models.py

@@ -44,17 +44,19 @@ class PydanticNode(BaseModel):
     value: int
     union_child: Union[PydanticNode, int]  # noqa: UP007
     list_child: List[PydanticNode]  # noqa: UP006
-    optional_child: Union[PydanticNode, None]  # noqa: UP007
+    optional_union_child: Union[PydanticNode, None]  # noqa: UP007
+    optional_child: Optional[PydanticNode]  # noqa: UP007
     child: PydanticNode = Field(default=_Sentinel)  # type: ignore[assignment]
 
 
 @pytest.mark.parametrize("factory_use_construct", (True, False))
 def test_recursive_pydantic_models(factory_use_construct: bool) -> None:
-    factory = ModelFactory.create_factory(PydanticNode)
+    factory = ModelFactory[PydanticNode].create_factory(PydanticNode)
 
     result = factory.build(factory_use_construct)
     assert result.child is _Sentinel, "Default is not used"  # type: ignore[comparison-overlap]
     assert isinstance(result.union_child, int)
+    assert result.optional_union_child is None
     assert result.optional_child is None
     assert result.list_child == []