Error in 0.0ms

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019067 +o rules:numerics
(FPCore (NdChar Ec Vef EDonor mu KbT NaChar Ev EAccept)
  :name "Bulmash initializePoisson"
  (+ (/ NdChar (+ 1 (exp (/ (- (- (- (- Ec Vef) EDonor) mu)) KbT)))) (/ NaChar (+ 1 (exp (/ (+ (+ (+ Ev Vef) EAccept) (- mu)) KbT))))))

Backtrace

build-list: contract violation expected: exact-nonnegative-integer? given: '(0)LC
build-list/opt/racket-7.0/collects/racket/private/list.rkt2962
debug-print/data/pavpan/nightlies/herbie/develop/src/debug.rkt1070
run-improve43/data/pavpan/nightlies/herbie/develop/src/mainloop.rkt3460
(unnamed)/opt/racket-7.0/collects/racket/private/more-scheme.rkt26128
run/opt/racket-7.0/share/pkgs/profile-lib/main.rkt392
profile-thunk16/opt/racket-7.0/share/pkgs/profile-lib/main.rkt90
(unnamed)/opt/racket-7.0/collects/racket/private/more-scheme.rkt26128