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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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)