def _hash_pair(first: bytes, second: bytes) -> bytes:
    """ Computes the hash of the items in lexicographic order """
    if first is None:
        return second

    if second is None:
        return first

    if first > second:
        return keccak(second + first)
    else:
        return keccak(first + second)
Computes the hash of the items in lexicographic order