The value NIL is not of type STRING when binding STRING

[Paul F. Dietz]

(lambda (b)
  (case b ((102 #\/ #\X #\z #\T #\g #\| #\W) 0) (t 0)))

==>

The value
  NIL
is not of type
  STRING
when binding STRING
   [Condition of type TYPE-ERROR]

Restarts:
 0: [RETRY] Retry SLIME REPL evaluation request.
 1: [*ABORT] Return to SLIME's top level.
 2: [ABORT] abort thread (#<THREAD tid=1885 "repl-thread" RUNNING {1000F10003}>)

Backtrace:
  0: (SB-IMPL::%READ-FROM-STRING NIL T NIL 0 NIL NIL) [external]
  1: ((FLET "THUNK" :IN SB-C:MAKE-PERFECT-HASH-LAMBDA))
  2: (SB-IMPL::%WITH-STANDARD-IO-SYNTAX #<FUNCTION (FLET "THUNK" :IN SB-C:MAKE-PERFECT-HASH-LAMBDA) {7FE3030BD67B}>)
  3: (SB-C:MAKE-PERFECT-HASH-LAMBDA #(87 124 103 84 122 88 ...) #<unused argument> T NIL T)
  4: (SB-C::EXPAND-HASH-CASE-FOR-JUMP-TABLE (#\W #\| #\g #\T #\z #\X ...) ((102 #\/ #\X #\z #\T #\g ...)) NIL #(0) T NIL)
  5: ((SB-C:DEFTRANSFORM SB-C:CASE-TO-JUMP-TABLE) #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME SB-C:CASE-TO-JUMP-TABLE :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WH..
  6: (SB-C::IR1-OPTIMIZE-COMBINATION #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::GLOBAL-VAR :%SOURCE-NAME SB-C:CASE-TO-JUMP-TABLE :TYPE #1=#<SB-KERNEL:FUN-TYPE #> :DEFINED-TYPE #1# :WHERE-FROM :DEC..
  7: (SB-C::IR1-OPTIMIZE #<SB-C:COMPONENT :NAME "<unknown>" {10082C57E3}> NIL)
  8: (SB-C::IR1-OPTIMIZE-UNTIL-DONE #<SB-C:COMPONENT :NAME "<unknown>" {10082C57E3}>)
  9: (SB-C::IR1-OPTIMIZE-PHASE-1 #<SB-C:COMPONENT :NAME "<unknown>" {10082C57E3}>)
 10: (SB-C::IR1-PHASES #<SB-C:COMPONENT :NAME "<unknown>" {10082C57E3}>)
 11: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "<unknown>" {10082C57E3}>)
 12: (SB-C::%COMPILE (LAMBDA (B) (CASE B (# 0) (T 0))) NIL NIL)
[...]

x86-64, "2.4.2.239-fc3445039"