in src/main/java/org/apache/sling/tooling/lc/git/GitChangeLogFinder.java [81:88]
private Ref getTagChecked(Repository repository, String artifactId, String version) throws IOException {
final String tagName = artifactId + "-" + version;
final Ref ref = repository.getRefDatabase().findRef(Constants.R_TAGS + tagName);
if (ref == null)
throw new RuntimeException("No tag " + tagName + " found in git repo at " + repository.getDirectory());
return ref;
}