DeprecationWarning: Sentinel is not a public part of the traitlets API (from traittypes) #1624

bqplot/__init__.py:64: in <module>
    from .figure import *  # noqa
bqplot/figure.py:36: in <module>
    from .interacts import Interaction
bqplot/interacts.py:41: in <module>
    from traittypes import Array
traittypes/__init__.py:1: in <module>
    from .traittypes import *
traittypes/traittypes.py:20: in <module>
    Empty = Sentinel('Empty', 'traittypes',
traitlets/__init__.py:24: in __init__
    warn(
traitlets/utils/warnings.py:11: in warn
    return warnings.warn(msg, category=category, stacklevel=stacklevel, source=source)
E   DeprecationWarning:
E               Sentinel is not a public part of the traitlets API.
E               It was published by mistake, and may be removed in the future.