Steel Bank Common Lisp

I'm trying to poll a socket for incoming connections using
SOCKET-ACCEPT, but, AFAICT, SOCKET-ACCEPT either signals a
SOCKET-ERROR or returns a socket on success.  Should I be using a
different function?  Would it be convenient for SOCKET-ACCEPT to
return NIL if no connection is available for non-blocking sockets?  Or
is the signalled condition meant to be handled to see if it's an error
or if no connections are present?

        Thanks in advance for any help,

                        --Tony