docs: public ClassInfo getSuperclass() {
          final Set<ClassInfo> superClasses = relatedClasses.get(RelType.SUPERCLASSES);
          if (superClasses == null || superClasses.isEmpty()) {
              return null;
          } else if (superClasses.size() > 2) {
              throw new IllegalArgumentException("More than one superclass: " + superClasses);
          } else {
              final ClassInfo superclass = superClasses.iterator().next();
              if (superclass.getName().equals("java.lang.Object")) {
                  return null;
              } else {
                  return superclass;
              }
          }
      }