VMS Help TCPIP Services, Programming Interfaces, RPC XDR Routines, xdr_void, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine is used as a placeholder for a program that passes
    no data in a remote procedure call. Most client and server
    routines expect an XDR routine to be called, even when there
    is no data to pass.