def unset_default_sampler():
    """Resets the default sampler back to None.

    Examples
    --------
    This example sets sampler0 as the default sampler, verifies the setting,
    then resets the default, and verifies the resetting.

    >>> dnx.set_default_sampler(sampler0)  # doctest: +SKIP
    >>> print(dnx.get_default_sampler())  # doctest: +SKIP
    'sampler0'
    >>> dnx.unset_default_sampler()  # doctest: +SKIP
    >>> print(dnx.get_default_sampler())  # doctest: +SKIP
    None
    """
    global _SAMPLER
    _SAMPLER = None
