themeConfig.docs.sidebar options throws 'ValidationError: "docs.sidebar" is not allowed' on build

Question

I'm using Docusaurus 2.0.0-rc.1 and trying to add hideable: true and autoCollapseCategories: true options in docusaurus.config.js according to https://docusaurus.io/docs/sidebar#hideable-sidebar, but I've received an error during build:

> docusaurus build

[INFO] [en] Creating an optimized production build...
[ERROR] Unable to build website for locale en.
[ERROR] ValidationError: "docs.sidebar" is not allowed

My sidebars.js (autogenerated sidebar):

/** @type {import('@docusaurus/plugin-content-docs').SidebarsConfig} */
const sidebars = {
  DocSidebar: [{type: 'autogenerated', dirName: '.'}],
};

module.exports = sidebars;

My docusaurus.config.js:

// @ts-check
// Note: type annotations allow type checking and IDEs autocompletion

const lightCodeTheme = require('prism-react-renderer/themes/github');
const darkCodeTheme = require('prism-react-renderer/themes/dracula');

/** @type {import('@docusaurus/types').Config} */
const config = {
  title: 'Test portal',
  tagline: 'Test company',
  url: 'https://test.com',
  baseUrl: '/',
  onBrokenLinks: 'ignore',
  onBrokenMarkdownLinks: 'warn',
  favicon: 'img/favicon.ico',
  organizationName: 'Test.com', // Usually your GitHub org/user name.
  projectName: 'test-repo', // Usually your repo name.

  presets: [
    [
      'classic',
      /** @type {import('@docusaurus/preset-classic').Options} */
      ({
        docs: {
          lastVersion: 'current',
          versions: {
            current: {
              label: '1.1.0',
              path: '1.1.0',
              badge: true,
            },
          },
          sidebarPath: require.resolve('./sidebars.js'),
        },
        blog: false,
        theme: {
          customCss: require.resolve('./src/css/custom.css'),
        },
      }),
    ],
  ],

  themeConfig:
   /** @type {import('@docusaurus/preset-classic').ThemeConfig} */
    ({
       docs: {
        sidebar: {
          hideable: true,
          autoCollapseCategories: true,
        },
      },
      navbar: {
        title: 'Docs portal',
        logo: {
          alt: 'Company Logo',
          src: 'img/logo.png',
        },
        items: [
          {
            type: 'doc',
            docId: 'intro',
            position: 'left',
            label: 'Product docs',
          },
          {
            type: 'docsVersionDropdown',
            position: 'right',
            dropdownItemsAfter: [{to: '/versions', label: 'All versions'}],
            dropdownActiveClassDisabled: true,
          },
          {
          href: 'https://test.com',
          label: 'Test Company',
          position: 'right',
          },
        ],
      },
      footer: {
        style: 'dark',
         copyright: `Copyright © ${new Date().getFullYear()} Test Company Built with Docusaurus.`,
      },
      prism: {
        theme: lightCodeTheme,
        darkTheme: darkCodeTheme,
      },
    }),
};

module.exports = config;