}

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

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

    DummyHandler(TypeToken<?> interfaceType) {
      this.interfaceType = interfaceType;
    }

    @Override

  }

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

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

    DummyHandler(TypeToken<?> interfaceType) {
      this.interfaceType = interfaceType;
    }

    @Override