Runtime error running fmt

[samth]

This is at current head of samth/recspecs,ce25f983c7fece4cdf216159b609484c03d8b39a

789d993ae6da:/workspace/recspecs# ../racket/bin/raco fmt -i recspecs-lib/ma
in.rkt
root@789d993ae6da:/workspace/recspecs# ../racket/bin/raco fmt -i recspecs/main.s
crbl recspecs/tests/capture-output.rkt recspecs/tests/ocaml-tests.rkt recspecs/t
ests/property-capture-output.rkt recspecs/tests/stderr.rkt
string-contains?: contract violation
  expected: string?
  given: #""
  context...:
   /root/.local/share/racket/8.17/pkgs/fmt/params.rkt:36:0: app-prefix?
   /root/.local/share/racket/8.17/pkgs/fmt/params.rkt:23:3
   /root/.local/share/racket/8.17/pkgs/fmt/core.rkt:132:2: format-#%app
   /workspace/racket/collects/racket/private/more-scheme.rkt:377:2: hash-ref!
   .../private/map.rkt:40:19: loop
   [repeats 48 more times]
   /root/.local/share/racket/8.17/pkgs/fmt/core.rkt:53:0: pretty-doc
   /root/.local/share/racket/8.17/pkgs/fmt/main.rkt:54:5
   /root/.local/share/racket/8.17/pkgs/fmt/main.rkt:44:0: program-format
   /workspace/racket/collects/racket/contract/private/arrow-val-first.rkt:555:3
   /root/.local/share/racket/8.17/pkgs/fmt/raco.rkt:136:0
   body of "/root/.local/share/racket/8.17/pkgs/fmt/raco.rkt"
   /workspace/racket/collects/raco/raco.rkt:41:0
   body of "/workspace/racket/collects/raco/raco.rkt"
   body of "/workspace/racket/collects/raco/main.rkt"