in src/main/java/org/apache/maven/plugins/artifact/buildinfo/ReferenceBuildinfoUtil.java [301:312]
private File getReference(String groupId, File file) throws IOException {
File dir;
if (groupId == null) {
dir = referenceDir;
} else {
dir = new File(referenceDir, groupId);
if (!dir.isDirectory()) {
Files.createDirectories(dir.toPath());
}
}
return new File(dir, file.getName());
}