Entnext and Error with LSELSETP

I'm trying to use the following routine to create a virgin set of closed
polylines. I can't figure out the error I'm getting, "Error, bad argument
type: LSELSETP nil".
Len Miller

(defun CreateNewBounds (OldBounds );;/ LastEnt EntSS)
(setq LastEnt (entlast)
EntSS (ssadd)
)
(command "._-boundary" MidX "")
(while (setq LastEnt (entnext LastEnt))
(setq EntSS (ssadd LastEnt EntSS))
)
(command "_.erase"
OldBounds
""
)
(setq PolysWithin EntSS)
)

;;;First, Create one polyline rectangle, then offset
;;;it some arbitrary distance, outside or inside, to
;;;make the second one.
;;;Pick them both as OldSet
(setq MidX (getpoint "Pick inside, between the rectangles"))
(setq OldSet (ssget))
(CreateNewBounds OldSet)

 

When you do:
(setq LastEnt (entlast) EntSS (ssadd))
..you get only (1) entity, the 'last' in var LastEnt.
Then, when doing:
(while (setq LastEnt (entnext LastEnt))
(setq EntSS (ssadd LastEnt EntSS))
)
.......
you get nil in var LastEnt..no entnext exists 'after'
LastEnt..
Hence, downhill from there.

Bob

 

Thanks to a snippet I borrowed from a Joe Burke post, replace the following
three lines with what follows:

(while (setq LastEnt (entnext LastEnt))
(setq EntList (entget LastEnt))
(if
(and
(not
(wcmatch (cdr (assoc 0 EntList))
"ATTRIB,VERTEX,SEQEND"
)
)
(eq (cdr (assoc 410 EntList)) (getvar "ctab"))
)
(ssadd LastEnt EntSS)
)
)