API: serde fix nullable fields should be allowed to be none

pkgs/clan-cli/clan_cli/api/serde.py

@@ -127,6 +127,11 @@ def construct_value(t: type, field_value: JsonValue, loc: list[str] = []) -> Any
     """
     if t is None and field_value:
         raise ClanError(f"Expected None but got: {field_value}", location=f"{loc}")
+
+    if is_type_in_union(t, type(None)) and field_value is None:
+        # Sometimes the field value is None, which is valid if the type hint allows None
+        return None
+
     # If the field is another dataclass
     # Field_value must be a dictionary
     if is_dataclass(t) and isinstance(field_value, dict):
@@ -160,9 +165,9 @@ def construct_value(t: type, field_value: JsonValue, loc: list[str] = []) -> Any
     # Union types construct the first non-None type
     elif is_union_type(t):
         # Unwrap the union type
-        t = unwrap_none_type(t)
+        inner = unwrap_none_type(t)
         # Construct the field value
-        return construct_value(t, field_value)
+        return construct_value(inner, field_value)
 
     # Nested types
     # list

pkgs/clan-cli/tests/test_deserializers.py

@@ -244,6 +244,27 @@ def test_alias_field_from_orig_name() -> None:
         from_dict(Person, data)
 
 
+def test_none_or_string() -> None:
+    """
+    Field declares an alias. But the data is provided with the field name.
+    """
+
+    data = None
+
+    @dataclass
+    class Person:
+        name: Path
+
+    checked = from_dict(str | None, data)
+    assert checked is None
+
+    checked2 = from_dict(dict[str, str] | None, data)
+    assert checked2 is None
+
+    checked3 = from_dict(Person | None, data)
+    assert checked3 is None
+
+
 def test_path_field() -> None:
     @dataclass
     class Person: