When publishing a package, files are taken from the package root. However, additional sources, like build-generated files (e.g., .jar), may need inclusion. For instance, when publishing a UDF, metadata is stored in the root, while the UDF itself is compiled into a .jar in the target folder. Instead of using a separate script to assemble the package before publishing, it is more robust to include additional sources directly in the package.json. See an example here.