Fix edge case where DataStream[None, None] was not allowed

Author: bruno-f-cruz

src/contraqctor/contract/base.py

@@ -59,15 +59,15 @@ def __init__(
         name: str,
         *,
         description: Optional[str] = None,
-        reader_params: Optional[_typing.TReaderParams] = None,
+        reader_params: _typing.TReaderParams = _typing.UnsetParams,
         **kwargs,
     ) -> None:
         if "::" in name:
             raise ValueError("Name cannot contain '::' character.")
         self._name = name
 
         self._description = description
-        self._reader_params = reader_params if reader_params is not None else _typing.UnsetParams
+        self._reader_params = reader_params
         self._data = _typing.UnsetData
         self._parent: Optional["DataStream"] = None