Building with SBCL

[Slids]

When building decode.lisp with SBCL getting the error:
; file: /flexi-streams/decode.lisp
; in:
; DEFINE-CHAR-DECODERS (FLEXI-UTF-16-LE-FORMAT FLEXI-CR-UTF-16-LE-FORMAT FLEXI-CRLF-UTF-16-LE-FORMAT)
; (FLEXI-STREAMS::READ-NEXT-BYTE)
; --> PROG1 LET OR LET IF COND IF THE RETURN-FROM
; ==>
; NIL
;
; caught STYLE-WARNING:
; This is not a (MOD 1114112):
; NIL
; See also:
; The SBCL Manual, Node "Handling of Types"
ERROR: FAIL: SB-INT:TYPE-STYLE-WARNING 'This is not a (MOD 1114112):
NIL
See also:
The SBCL Manual, Node "Handling of Types"'

This happens for all the char-decoders that return nil, see:
(macrolet ((read-next-byte ()
`(prog1
(or octet-getter
(cond (first-octet-seen
(return-from char-decoder
(recover-from-encoding-error format
"End of data while in UTF-8 sequence.")))
(t (return-from char-decoder nil))))
(setq first-octet-seen t))))

[Slids]

Comes from removing the safety 0 settings in specials.lsip