@SuppressWarnings("unchecked") // interfaceType is T
    T result = (T) dummy;
    return result;
  }

  /** Returns the dummy return value for {@code returnType}. */
  abstract <R> @Nullable R dummyReturnValue(TypeToken<R> returnType);

  private final class DummyHandler extends AbstractInvocationHandler implements Serializable {
    private final TypeToken<?> interfaceType;

    DummyHandler(TypeToken<?> interfaceType) {

    @SuppressWarnings("unchecked") // interfaceType is T
    T result = (T) dummy;
    return result;
  }

  /** Returns the dummy return value for {@code returnType}. */
  abstract <R> @Nullable R dummyReturnValue(TypeToken<R> returnType);

  private final class DummyHandler extends AbstractInvocationHandler implements Serializable {
    private final TypeToken<?> interfaceType;

    DummyHandler(TypeToken<?> interfaceType) {

    } else {
      return TypeToken.of(Object.class);
    }
  }

  private <T> T newDefaultReturningProxy(TypeToken<T> type) {
    return new DummyProxy() {
      @Override
      <R> @Nullable R dummyReturnValue(TypeToken<R> returnType) {
        return getDefaultValue(returnType);
      }
    }.newProxy(type);
  }

  private static Invokable<?, ?> invokable(@Nullable Object instance, Method method) {

    private final transient ClassSanityTester tester;

    SerializableDummyProxy(ClassSanityTester tester) {
      this.tester = tester;
    }

    @Override
    <R> R dummyReturnValue(TypeToken<R> returnType) {
      return tester.getDummyValue(returnType);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return obj instanceof SerializableDummyProxy;
    }

    } else {
      return TypeToken.of(Object.class);
    }
  }

  private <T> T newDefaultReturningProxy(TypeToken<T> type) {
    return new DummyProxy() {
      @Override
      <R> @Nullable R dummyReturnValue(TypeToken<R> returnType) {
        return getDefaultValue(returnType);
      }
    }.newProxy(type);
  }

  private static Invokable<?, ?> invokable(@Nullable Object instance, Method method) {

    private final transient ClassSanityTester tester;

    SerializableDummyProxy(ClassSanityTester tester) {
      this.tester = tester;
    }

    @Override
    <R> R dummyReturnValue(TypeToken<R> returnType) {
      return tester.getDummyValue(returnType);
    }

    @Override
    public boolean equals(@Nullable Object obj) {
      return obj instanceof SerializableDummyProxy;
    }