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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 atlas_peer_is_whitelisted( peer_hostport, peer_table=None ):
 """ Is a peer whitelisted """

    ret = None
    with AtlasPeerTableLocked(peer_table) as ptbl:
        if peer_hostport not in ptbl.keys():
            return None 

        ret = ptbl[peer_hostport].get("whitelisted", False)

    return ret