The value NIL is not of type SB-ASSEM:LABEL when binding SB-C::TARGET-LABEL

[Paul F. Dietz]

(lambda (a b)
  (declare (type (integer 486 499) a))
  (case a
    ((-3 -1 4 3)
     (case b
       ((-4) b)
       ((-1) a)
       ((6 14) 0)
       (t b)))
    (t a)))

==>

The value
  NIL
is not of type
  SB-ASSEM:LABEL
when binding SB-C::TARGET-LABEL
   [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=3890 "repl-thread" RUNNING {1000F08003}>)

Backtrace:
  0: ((LAMBDA (SB-C::X) :IN SB-C::IR2-OPTIMIZE-JUMPS) NIL)
  1: ((FLET SB-IMPL::F :IN SB-IMPL::VECTOR-MAP-INTO/SIMPLE-VECTOR) NIL)
  2: (SB-KERNEL:%MAP-FOR-EFFECT-ARITY-1 #<FUNCTION (FLET SB-IMPL::F :IN SB-IMPL::VECTOR-MAP-INTO/SIMPLE-VECTOR) {7FA5E840D90B}> #(#1=#<SB-ASSEM:LABEL 1> #1# NIL #<SB-ASSEM:LABEL 2>))
  3: (SB-KERNEL:%MAP NIL #<FUNCTION (FLET SB-IMPL::F :IN SB-IMPL::VECTOR-MAP-INTO/SIMPLE-VECTOR) {7FA5E840D90B}> #(#1=#<SB-ASSEM:LABEL 1> #1# NIL #<SB-ASSEM:LABEL 2>)) [more]
  4: (SB-IMPL::VECTOR-MAP-INTO/SIMPLE-VECTOR #(#1=#<SB-ASSEM:LABEL 1> #1# 0 0) 0 4 #<FUNCTION (LAMBDA (SB-C::X) :IN SB-C::IR2-OPTIMIZE-JUMPS) {549F1B3B}> #(#1=#<SB-ASSEM:LABEL 1> #1# NIL #<SB-ASSEM:LABEL 2..
  5: (SB-C::IR2-OPTIMIZE-JUMPS #<SB-C:COMPONENT :NAME "<unknown>" {100B19C1C3}>)
  6: (SB-C::IR2-OPTIMIZE #<SB-C:COMPONENT :NAME "<unknown>" {100B19C1C3}> SB-C::REGALLOC)
  7: (SB-C::%COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "<unknown>" {100B19C1C3}>)
  8: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME "<unknown>" {100B19C1C3}>)
  9: (SB-C::%COMPILE (LAMBDA (A B) (DECLARE (TYPE # A)) (CASE A (# #) (T A))) NIL NIL)
[...]

x86-64, "2.4.2.199-8d98d5898"