Juvix mode makes magit diffing fail

[mariari]

This behaviour is observed in magit-ediff-dwim

You can observe this by trying to resolve a conflict in a juvix file.

Here is a stack trace

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  call-process("juvix" nil (#<buffer  *temp*> "/tmp/temporary-stderr-filehbm8FK") nil "--no-colors" "dev" "highlight" nil)
  apply(call-process "juvix" nil (#<buffer  *temp*> "/tmp/temporary-stderr-filehbm8FK") nil ("--no-colors" "dev" "highlight" nil))
  juvix-call(#<buffer  *temp*> "dev" "highlight" nil)
  apply(juvix-call #<buffer  *temp*> ("dev" "highlight" nil))
  juvix-call-read("dev" "highlight" nil)
  juvix-load()
  #f(compiled-function () #<bytecode -0x11a3b460c514261>)()
  run-hooks(change-major-mode-after-body-hook prog-mode-hook juvix-mode-hook)
  apply(run-hooks (change-major-mode-after-body-hook prog-mode-hook juvix-mode-hook))
  run-mode-hooks(juvix-mode-hook)
  juvix-mode()
  smerge-ediff()
  magit-ediff-resolve-rest("Package.juvix")
  magit-ediff-dwim()
  funcall-interactively(magit-ediff-dwim)
  call-interactively(magit-ediff-dwim nil nil)
  command-execute(magit-ediff-dwim)