return null;
            }
        };
    }

    static <T extends Throwable> void uncheckedThrow(Throwable t) throws T {
        throw (T) t; // rely on vacuous cast
    }

    private Model fireEvent(
            Model model,
            ModelBuilderRequest request,
            ModelProblemCollector problems,

            return null;
        }
    }

    @SuppressWarnings("unchecked")
    static <T extends Throwable> void uncheckedThrow(Throwable t) throws T {
        throw (T) t; // rely on vacuous cast
    }

    static class LazyMap<K, V> extends AbstractMap<K, V> {
        private final Supplier<Map<K, V>> supplier;
        private volatile Map<K, V> delegate;