import re


def _remove_chars(chars, s):
    """
    :param chars: string of characters to remove.
    :param s: input string
    :rtype: str

    >>> _remove_chars(string.punctuation, 'OLI_TIRS+')
    'OLITIRS'
    >>> _remove_chars('_', 'A_B_C')
    'ABC'
    >>> _remove_chars(string.punctuation, None)
    """
    if not s:
        return s
    return re.sub('[' + re.escape(''.join(chars)) + ']', '', s)