NAME
    isnull - whether a value is a null value

SYNOPSIS
    isnull(x)

TYPES
    x		any, &any

    return	int

DESCRIPTION
    Determine if x is a null value.  This function will return 1 if x is
    a null value, 0 otherwise.

EXAMPLE
    > mat a[2]
    > print isnull(a), isnull(1)
    1 0

LIMITS
    none

LIBRARY
    none

SEE ALSO
    isassoc, isatty, isblk, isconfig, isdefined, iserror, iseven, isfile,
    ishash, isident, isint, islist, ismat, ismult, isnum, isobj,
    isobjtype, isodd, isprime, isrand, israndom, isreal, isrel,
    issimple, issq, isstr, istype