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, isfile, isident, isint, islist, ismat, isnum, isobj,
    isreal, isstr, issimple, istype