clack-handler-fcgi error

[ghost]

(ql:quickload :clack)
;To load "clack":
;  Load 1 ASDF system:
;    clack
; Loading "clack"
;.
;(:CLACK)

(defun app (env)
 `(200 (:content-type "text/plain") ("common lisp")))
; in: DEFUN APP
;     (SB-INT:NAMED-LAMBDA APP
;         (ENV)
;       (BLOCK APP `(200 (:CONTENT-TYPE "text/plain") ("hello"))))
;
; caught STYLE-WARNING:
;   The variable ENV is defined but never used.
;
; compilation unit finished
;   caught 1 STYLE-WARNING condition
;APP

(clack:clackup 'app :server :fcgi)

;Fcgi server is started.
;Listening on 127.0.0.1:5000.
;#S(CLACK.HANDLER::HANDLER
;   :SERVER :FCGI
;   :ACCEPTOR #<SB-THREAD:THREAD "clack-handler-fcgi" RUNNING {1002A01A13}>)
;
;debugger invoked on a TYPE-ERROR in thread
;#<THREAD "clack-handler-fcgi" RUNNING {1002A01A13}>:
;  The value
;    NIL
;  is not of type
;    (OR (VECTOR CHARACTER) (VECTOR NIL) BASE-STRING
;        (SIMPLE-ARRAY (UNSIGNED-BYTE 8) (*)))
;
;  when binding QURI.DECODE::DATA
;
;The current thread is not at the foreground,
;SB-THREAD:RELEASE-FOREGROUND has to be called in #<SB-THREAD:THREAD "main thread" RUNNING {1001560103}>
;for this thread to enter the debugger.

;what i did wrong ;please help