test_initial_values failure

[bcdarwin]

Building traittypes 0.2.3 against Nixpkgs master (python 3.12 or 3.13, traitlets 5.14.3, pandas 2.3.1, numpy 2.3.3, xarray 2025.07.1, pytest 8.4.2) produces:

 ...
       >=================================== FAILURES ===================================
       >________________________ TestSeries.test_initial_values ________________________
       > self = <traittypes.tests.test_traittypes.TestSeries testMethod=test_initial_values>
       >
       >     def test_initial_values(self):
       >         class Foo(HasTraits):
       >             a = Series()
       >             b = Series(None, allow_none=True)
       >             c = Series([])
       >             d = Series(Undefined)
       >         foo = Foo()
       > >       self.assertTrue(foo.a.equals(pd.Series()))
       > E       AssertionError: False is not true
       >
       > traittypes/tests/test_traittypes.py:169: AssertionError
       > =============================== warnings summary ===============================
       > traittypes/tests/test_traittypes.py::TestArray::test_initial_values
       > traittypes/tests/test_traittypes.py::TestDataFrame::test_initial_values
       > traittypes/tests/test_traittypes.py::TestDataset::test_initial_values
       > traittypes/tests/test_traittypes.py::TestDataArray::test_initial_values
       >   /nix/store/adzmxpxd1g25i92sfj9zw29gppj08i3v-python3.13-traitlets-5.14.3/lib/python3.13/site-packages/traitlets/traitlets.py:637: DeprecationWarning: Explicit using of Undefined as the default value is deprecated in traitlets 5.0, and may cause exceptions in the future.
       >     warn(
       >
       > -- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
       > =========================== short test summary info ============================
       > FAILED traittypes/tests/test_traittypes.py::TestSeries::test_initial_values - AssertionError: False is not true
       > =================== 1 failed, 25 passed, 4 warnings in 0.80s ===================