Compiling Copybara through Bazel

I am currently trying to compile Copybara using the workspace additions recommended in the `README.md` with the following command:

`bazel build @com_github_google_copybara//java/com/google/copybara`

I am seeing the following issue:

```
external/io_bazel/src/main/java/net/starlark/java/eval/Dict.java:462: error: cannot find symbol
var dict = (Dict) m;
^
symbol: class var
location: class Dict
where K,V are type-variables:
K extends Object declared in class Dict
V extends Object declared in class Dict
```

Is there a specific toolchain that copybara developers recommend when building this in bazel?