code: boolean addRelatedClass(final RelType relType, final ClassInfo classInfo) {
          Set<ClassInfo> classInfoSet = relatedClasses.get(relType);
          if (classInfoSet == null) {
              relatedClasses.put(relType, classInfoSet = new LinkedHashSet<>(4));
          }
          return classInfoSet.add(classInfo);
      }
docs: Add a class with a given relationship type. Return whether the collection changed as a result of the call.
  
  @param relType
  the {@link RelType}
  @param classInfo
  the {@link ClassInfo}
  @return true, if successful