set-exclusive-or triggers a warning when compiled with (space 0)

[Jerome Abela]

(declaim (optimize (compilation-speed 0) (speed 0) (space 0) (debug 3)))

(defun set-not-equal (set1 set2)
  (set-exclusive-or set1 set2))

; in: DEFUN SET-NOT-EQUAL
; (SET-EXCLUSIVE-OR JACK-CORE::SET1 JACK-CORE::SET2)
;
; caught WARNING:
; Derived type of SB-IMPL::TEST is
; (VALUES NULL &OPTIONAL),
; conflicting with its asserted type
; FUNCTION.
; See also:
; The SBCL Manual, Node "Handling of Types"
;
; compilation unit finished
; caught 1 WARNING condition

SBCL 2.1.6 on macOS