Fix from_dict for Optional values in collections

serde/de.py

@@ -737,7 +737,11 @@ def __getitem__(self, n: int) -> DeField[Any] | InnerField[Any]:
             return InnerField(typ, f"{self.data}[{n}]", datavar=f"{self.data}[{n}]", **opts)
         else:
             # For Optional etc.
-            return DeField(
+            # Preserve InnerField when unwrapping Optional inside a collection,
+            # so that data access uses the loop variable directly (e.g. "v")
+            # instead of indexing into it (e.g. v["v"]).
+            field_cls = type(self)
+            return field_cls(
                 typ,
                 self.name,
                 datavar=self.datavar,
@@ -1001,7 +1005,7 @@ def opt(self, arg: DeField[Any]) -> str:
         Render rvalue for Optional.
         """
         inner = arg[0]
-        if arg.iterbased:
+        if arg.iterbased or isinstance(arg, InnerField):
             exists = f"{arg.data} is not None"
         elif arg.flatten:
             # Check nullabilities of all nested fields.

tests/test_union.py

@@ -919,3 +919,20 @@ class Baz:
     all_false_json = '{"num": {"all": false}}'
     with pytest.raises(SerdeError):
         from_json(Baz, all_false_json)
+
+
+def test_optional_value_in_list():
+    """Test that Optional/Union with None in list values deserializes correctly."""
+
+    @serde
+    @dataclass
+    class Inner:
+        value: int = 10
+
+    @serde
+    @dataclass
+    class Outer:
+        items: list[Optional[Inner]]
+
+    instance = Outer(items=[Inner(value=1), None, Inner(value=3)])
+    assert from_dict(Outer, to_dict(instance)) == instance