def strip_prefix(s, prefix):
    """Remove prefix frm the beginning of s
    is s = "some_something" and prefix = "some_", return "something"
    if s is not a string return None
    if prefix is not a string, return s

    :param str s: string to modify
    :param str prefix: prefix to remove

    :rtype: Optional[str]=None
    """
    if not isinstance(s, str):
        return None
    if not isinstance(prefix, str):
        return s
    if s.startswith(prefix):
        return s[len(prefix) :]  # noqa: E203
    return s