def value_to_none(config_val, evar):
    """
    Given a value that evaluates to a boolean False, return None.

    :param str config_val: The env var value.
    :param EnvironmentVariable evar: The EVar object we are validating
        a value for.
    :rtype: str or None
    :return: Either the non-False value or None.
    """
    if not config_val:
        return None
    return config_val
