GitHub Actions cache restored but not present

I’m trying to use actions/cache@v2 for caching build results (Isabelle Heaps in this case).
You can see the code via this link.

In Cache Isabelle Heaps step, actions/cache@v2 says that the cache hits for path .heaps, but the directory is not present in the subsequent steps. For example, the Show heap cache dir step shows the working directory and .heaps directory is not present.

How can I have the specified directory present in the build steps? Thanks.

Hmm… It seems that I was misunderstanding the path syntax.
Originally, I had:

- name: Cache Isabelle Heaps
  uses: actions/cache@v2
  with:
    path: |
      - .heaps

But the correct syntax is:

- name: Cache Isabelle Heaps
  uses: actions/cache@v2
  with:
    path: .heaps