compilation fails

[klartext]

$ git log --oneline
eb71e68 (HEAD -> master, origin/master, origin/HEAD) Upgrade to opam v2.0
27945c6 Add annotation to ensure tail recursive call
2dc8992 Add Cmd/Sub map functionality to support modules
4b9ef2a Add support for multiple subscriptions of same type
c59b9e8 Ignore opam prepare folders
9eb2615 Remove install section from opam file
e5db904 (tag: 0.1.0) Relax contraints on dependencies
467af46 Downgrade to opam v1.2
b2ee1e0 Initial version
$ git status
On branch master
Your branch is up to date with 'origin/master'.

nothing to commit, working tree clean
$ make
dune build
File "src/sub.ml", line 20, characters 11-25:
20 | module M = Misc.StringMap
                ^^^^^^^^^^^^^^
Error: Unbound module Misc.StringMap
make: *** [Makefile:6: build] Error 1
$