in src/main/java/org/apache/maven/archiver/MavenArchiver.java [217:223]
private void addManifestAttribute(Manifest manifest, Map<String, String> map, String key, String value)
throws ManifestException {
if (map.containsKey(key)) {
return; // The map value will be added later
}
addManifestAttribute(manifest, key, value);
}