docs: public ClassInfoList union(final ClassInfoList... others) {
          final Set<ClassInfo> reachableClassesUnion = new LinkedHashSet<>(this);
          final Set<ClassInfo> directlyRelatedClassesUnion = new LinkedHashSet<>(directlyRelatedClasses);
          for (final ClassInfoList other : others) {
              reachableClassesUnion.addAll(other);
              directlyRelatedClassesUnion.addAll(other.directlyRelatedClasses);
          }
          return new ClassInfoList(reachableClassesUnion, directlyRelatedClassesUnion, sortByName);
      }