check(Files.isDirectory(dir)) { "Must be a directory" }
                    Files.walkFileTree(dir, object : SimpleFileVisitor<Path>() {
                        override fun visitFile(file: Path, attrs: BasicFileAttributes): FileVisitResult {
                            val entryName = dir.relativize(file).joinToString(separator = "/") { it.toString() }
                            jarStream.putNextEntry(JarEntry(entryName))