in src/main/java/org/apache/maven/plugin/resources/remote/ModelUtils.java [270:281]
public static List<Repository> mergeRepositoryLists(List<Repository> dominant, List<Repository> recessive) {
List<Repository> repositories = new ArrayList<>(dominant);
for (Repository repository : recessive) {
if (!repositories.contains(repository)) {
repositories.add(repository);
}
}
return repositories;
}