Fixes catchall inheritance issue (#500)

dataclasses_json/undefined.py

@@ -198,7 +198,7 @@ def _get_default(catch_all_field: Field) -> Any:
     @staticmethod
     def handle_to_dict(obj, kvs: Dict[Any, Any]) -> Dict[Any, Any]:
         catch_all_field = \
-            _CatchAllUndefinedParameters._get_catch_all_field(obj)
+            _CatchAllUndefinedParameters._get_catch_all_field(obj.__class__)
         undefined_parameters = kvs.pop(catch_all_field.name)
         if isinstance(undefined_parameters, dict):
             kvs.update(

tests/test_undefined_parameters.py

@@ -383,4 +383,22 @@ class UnknownAPIDumpDefault:
         catch_all: CatchAll = field(default_factory=dict)
 
     dump = UnknownAPIDumpDefault(**valid_response)
-    assert dump.catch_all == {}
+    assert dump.catch_all == {}
+
+
+def test_undefined_inheritance():
+    @dataclass_json(undefined=Undefined.INCLUDE)
+    @dataclass
+    class TestInternalConfig:
+        options: CatchAll = None
+        val: str = "bar"
+        val2: int = 0
+
+    @dataclass_json
+    @dataclass
+    class TestInternalExtendConfig(TestInternalConfig):
+        val: str = "baz"
+
+    tie = TestInternalExtendConfig()
+    tie.to_dict()
+