code: static <K>
        MapMakerInternalMap<K, Dummy, ? extends InternalEntry<K, Dummy, ?>, ?> createWithDummyValues(
            MapMaker builder) {
      if (builder.getKeyStrength() == Strength.STRONG
          && builder.getValueStrength() == Strength.STRONG) {
        return new MapMakerInternalMap<>(builder, StrongKeyDummyValueEntry.Helper.<K>instance());
      }
      if (builder.getKeyStrength() == Strength.WEAK
          && builder.getValueStrength() == Strength.STRONG) {
        return new MapMakerInternalMap<>(builder, WeakKeyDummyValueEntry.Helper.<K>instance());
      }
      if (builder.getValueStrength() == Strength.WEAK) {
        throw new IllegalArgumentException("Map cannot have both weak and dummy values");
      }
      throw new AssertionError();
    }
docs: Returns a fresh {@link MapMakerInternalMap} with {@link MapMaker.Dummy} values but otherwise as
  specified by the given {@code builder}. The returned {@link MapMakerInternalMap} will be
  optimized to saved memory. Since {@link MapMaker.Dummy} is a singleton, we don't need to store
  any values at all. Because of this optimization, {@code build.getValueStrength()} must be
  {@link Strength#STRONG}.
  
  <p>This method is intended to only be used by the internal implementation of {@link Interners},
  since a map of dummy values is the exact use case there.