code: @GwtIncompatible("incompatible method")
      private static void register(final Object lhs, final Object rhs) {
          Set<Pair<IDKey, IDKey>> registry = getRegistry();
          if (registry == null) {
              registry = new HashSet<>();
              REGISTRY.set(registry);
          }
          final Pair<IDKey, IDKey> pair = getRegisterPair(lhs, rhs);
          registry.add(pair);
      }
docs: <p>
  Registers the given object pair.
  Used by the reflection methods to avoid infinite loops.
  </p>
  
  @param lhs <code>this</code> object to register
  @param rhs the other object to register