The value NIL is not of type SB-C::LVAR (in IR1-OPTIMIZE-IF)

[Paul F. Dietz]

 (defun bug013 (x y z)
  (when y
    (let* ((v (f1 x))
           (s (f2 v y z))
           (r (f3 v y z)))
      (let ((c
             (when (f4 v (f6 y) z) y))
            (left
             (when r (f5 x (f8 y) z)))
            (right
             (when (and r (not s))
               (f5 x (f7 y) z))))
        (cond
         (right
          (if c
              (cons c right)
              right)))))))

==>

The value
  NIL
is not of type
  SB-C::LVAR
   [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 "new-repl-thread" RUNNING {101C03D783}>)

Backtrace:
  0: ((FLET "LAMBDA0" :IN "SYS:SRC;COMPILER;IR1OPT.LISP"))
  1: (SB-C::%WITH-IR1-ENVIRONMENT-FROM-NODE #<SB-C::COMBINATION :FUN #<SB-C::REF :LEAF #<SB-C::CLAMBDA :%SOURCE-NAME SB-C::.ANONYMOUS. :%DEBUG-NAME # :KIND :LET :TYPE #<SB-KERNEL:BUILT-IN-CLASSOID FUNCTIO..
  2: ((FLET SB-C::DO-1-USE :IN SB-C::TENSION-IF-IF-1) #<SB-C::REF :%SOURCE-NAME NIL :LEAF #<SB-KERNEL:CONSTANT :VALUE NIL {101C1DF453}> {101C1F6323}>)
  3: (SB-C::IR1-OPTIMIZE-IF #<SB-C::CIF :TEST #<SB-C::REF :%SOURCE-NAME RIGHT :LEAF #<SB-C::LAMBDA-VAR :%SOURCE-NAME RIGHT {101C1DDC03}> {101C1DE9C3}> :CONSEQUENT #<SB-C::CBLOCK 7 :START c1 {101C1DE7A3}> :..
  4: (SB-C::IR1-OPTIMIZE #<SB-C:COMPONENT :NAME BUG013 {101C204DA3}> NIL)
  5: (SB-C::IR1-OPTIMIZE-UNTIL-DONE #<SB-C:COMPONENT :NAME BUG013 {101C204DA3}>)
  6: (SB-C::IR1-OPTIMIZE-PHASE-1 #<SB-C:COMPONENT :NAME BUG013 {101C204DA3}>)
  7: (SB-C::IR1-PHASES #<SB-C:COMPONENT :NAME BUG013 {101C204DA3}>)
  8: (SB-C::COMPILE-COMPONENT #<SB-C:COMPONENT :NAME BUG013 {101C204DA3}>)
  9: (SB-C::%COMPILE (SB-INT:NAMED-LAMBDA BUG013 (X Y Z) (BLOCK BUG013 (WHEN Y #))) #<SB-C::CORE-OBJECT {101C1CD993}> :NAME NIL :PATH (SB-C::ORIGINAL-SOURCE-START 0 0))