diff --git a/v2/lib/load/blog.js b/v2/lib/load/blog.js
index 1b95a7c8fe..b38087dc09 100644
--- a/v2/lib/load/blog.js
+++ b/v2/lib/load/blog.js
@@ -25,10 +25,10 @@ async function loadBlog({blogDir, env, siteConfig}) {
 
   const {baseUrl} = siteConfig;
 
-  /* Prepare metadata container */
+  // Prepare metadata container.
   const blogMetadatas = [];
 
-  /* the language for each blog page */
+  // Language for each blog page.
   const defaultLangTag = idx(env, ['translation', 'defaultLanguage', 'tag']);
 
   await Promise.all(
@@ -58,13 +58,13 @@ async function loadBlog({blogDir, env, siteConfig}) {
   );
   blogMetadatas.sort((a, b) => a.date - b.date);
 
-  // blogpage handling. Example: `/blog`, `/blog/page1`, `/blog/page2`
+  // Blog page handling. Example: `/blog`, `/blog/page1`, `/blog/page2`
   const perPage = 10;
   const numOfBlog = blogMetadatas.length;
   const numberOfPage = Math.ceil(numOfBlog / perPage);
   const basePageUrl = path.join(baseUrl, 'blog');
 
-  /* eslint-disable */
+  // eslint-disable-next-line
   for (let page = 0; page < numberOfPage; page++) {
     blogMetadatas.push({
       permalink: normalizeUrl([
diff --git a/v2/lib/load/docs/index.js b/v2/lib/load/docs/index.js
index 361f996a7a..1adcac79a9 100644
--- a/v2/lib/load/docs/index.js
+++ b/v2/lib/load/docs/index.js
@@ -19,7 +19,7 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
   // @tested - build the docs ordering such as next, previous, category and sidebar
   const order = createOrder(docsSidebars);
 
-  /* Settle versions & translations from environment */
+  // Settle versions & translations from environment.
   const translationEnabled = idx(env, ['translation', 'enabled']);
   const enabledLanguages =
     translationEnabled && idx(env, ['translation', 'enabledLanguages']);
@@ -30,19 +30,17 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
   const versions =
     (versioningEnabled && idx(env, ['versioning', 'versions'])) || [];
 
-  /* Prepare metadata container */
+  // Prepare metadata container.
   const docsMetadatas = {};
 
-  /* metadata for default docs files */
+  // Metadata for default docs files.
   const docsFiles = await globby(['**/*.md'], {
     cwd: docsDir,
   });
   await Promise.all(
     docsFiles.map(async source => {
-      /* 
-        Do not allow reserved version/ translated folder name in 'docs'
-        e.g: 'docs/version-1.0.0/' should not be allowed as it can cause unwanted bug
-      */
+      // Do not allow reserved version/ translated folder name in 'docs'
+      // e.g: 'docs/version-1.0.0/' should not be allowed as it can cause unwanted bug
       const subFolder = getSubFolder(path.resolve(docsDir, source), docsDir);
       const versionsFolders = versions.map(version => `version-${version}`);
       if ([...enabledLangTags, ...versionsFolders].includes(subFolder)) {
@@ -60,7 +58,7 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
     }),
   );
 
-  /* metadata for non-default-language docs */
+  // Metadata for non-default-language docs.
   if (translationEnabled) {
     const translatedDir = path.join(siteDir, 'translated_docs');
     const translatedFiles = await globby(['**/*.md'], {
@@ -68,7 +66,7 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
     });
     await Promise.all(
       translatedFiles.map(async source => {
-        /* 
+        /*
           Do not process disabled & default languages folder in `translated_docs`
           e.g: 'translated_docs/ja/**' should not be processed if lang 'ja' is disabled
         */
@@ -93,7 +91,7 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
     );
   }
 
-  /* metadata for versioned docs */
+  // Metadata for versioned docs.
   if (versioningEnabled) {
     const versionedDir = path.join(siteDir, 'versioned_docs');
     const versionedFiles = await globby(['**/*.md'], {
@@ -113,7 +111,7 @@ async function loadDocs({siteDir, docsDir, env, siteConfig}) {
     );
   }
 
-  /* Get the titles of the previous and next ids so that we can use them */
+  // Get the titles of the previous and next ids so that we can use them.
   Object.keys(docsMetadatas).forEach(currentID => {
     const previousID = idx(docsMetadatas, [currentID, 'previous']);
     if (previousID) {
diff --git a/v2/lib/load/docs/metadata.js b/v2/lib/load/docs/metadata.js
index 0885e3f978..6bbe02edcf 100644
--- a/v2/lib/load/docs/metadata.js
+++ b/v2/lib/load/docs/metadata.js
@@ -1,4 +1,4 @@
-/**
+/*
  * Copyright (c) 2017-present, Facebook, Inc.
  *
  * This source code is licensed under the MIT license found in the
@@ -11,6 +11,7 @@ const {getSubFolder, idx, parse, normalizeUrl} = require('../utils');
 
 function getLanguage(filepath, refDir, env) {
   const translationEnabled = idx(env, ['translation', 'enabled']);
+
   if (translationEnabled) {
     const detectedLangTag = getSubFolder(filepath, refDir);
     const enabledLanguages = idx(env, ['translation', 'enabledLanguages']);
@@ -19,18 +20,22 @@ function getLanguage(filepath, refDir, env) {
     if (langTags.includes(detectedLangTag)) {
       return detectedLangTag;
     }
+
     const defaultLanguage = idx(env, ['translation', 'defaultLanguage']);
     if (defaultLanguage && defaultLanguage.tag) {
       return defaultLanguage.tag;
     }
   }
-  return undefined;
+
+  return null;
 }
 
 function getVersion(filepath, refDir, env) {
   const versioningEnabled = idx(env, ['versioning', 'enabled']);
+
   if (versioningEnabled) {
     const subFolder = getSubFolder(filepath, refDir);
+
     if (subFolder) {
       const detectedVersion = subFolder.replace(/^version-/, '');
       const versions = idx(env, ['versioning', 'versions']) || [];
@@ -38,9 +43,11 @@ function getVersion(filepath, refDir, env) {
         return detectedVersion;
       }
     }
+
     return 'next';
   }
-  return undefined;
+
+  return null;
 }
 
 module.exports = async function processMetadata(
@@ -54,7 +61,7 @@ module.exports = async function processMetadata(
   const fileString = await fs.readFile(filepath, 'utf-8');
   const {metadata} = parse(fileString);
 
-  /* default id is the file name */
+  // Default id is the file name.
   if (!metadata.id) {
     metadata.id = path.basename(source, path.extname(source));
   }
@@ -62,17 +69,17 @@ module.exports = async function processMetadata(
     throw new Error('Document id cannot include "/".');
   }
 
-  /* default title is the id */
+  // Default title is the id.
   if (!metadata.title) {
     metadata.title = metadata.id;
   }
 
-  /* language */
+  // Language.
   const language = getLanguage(filepath, refDir, env);
   metadata.language = language;
   const langPart = (language && `${language}/`) || '';
 
-  /* version */
+  // Version.
   const defaultLangTag = idx(env, ['translation', 'defaultLanguage', 'tag']);
   let versionRefDir = refDir;
   if (language && language !== defaultLangTag) {
@@ -84,10 +91,8 @@ module.exports = async function processMetadata(
   const versionPart =
     (version && version !== latestVersion && `${version}/`) || '';
 
-  /* 
-    Convert temporarily metadata.id to the form of dirname/id without version/lang prefix
-    ex: file `versioned_docs/version-1.0.0/en/foo/bar.md` with id `version-1.0.0-bar` => `foo/bar`
-  */
+  // Convert temporarily metadata.id to the form of dirname/id without version/lang prefix.
+  // e.g.: file `versioned_docs/version-1.0.0/en/foo/bar.md` with id `version-1.0.0-bar` => `foo/bar`
   if (language) {
     metadata.id = metadata.id.replace(new RegExp(`^${language}-`), '');
   }
@@ -112,19 +117,15 @@ module.exports = async function processMetadata(
     }
   }
 
-  /* 
-    The docs absolute file source
-    e.g: `/end/docs/hello.md` or `/end/website/versioned_docs/version-1.0.0/hello.md` 
-  */
+  // The docs absolute file source.
+  // e.g: `/end/docs/hello.md` or `/end/website/versioned_docs/version-1.0.0/hello.md`
   metadata.source = path.join(refDir, source);
 
-  /* Build the permalink */
+  // Build the permalink.
   const {baseUrl, docsUrl} = siteConfig;
 
-  /* 
-    if user has own custom permalink defined in frontmatter
-    e.g: :baseUrl:docsUrl/:langPart/:versionPart/endiliey/:id
-  */
+  // If user has own custom permalink defined in frontmatter
+  // e.g: :baseUrl:docsUrl/:langPart/:versionPart/endiliey/:id
   if (metadata.permalink) {
     metadata.permalink = path.resolve(
       metadata.permalink
@@ -144,20 +145,20 @@ module.exports = async function processMetadata(
     ]);
   }
 
-  /* if version */
+  // If version.
   if (version && version !== 'next') {
     metadata.id = `version-${version}-${metadata.id}`;
   }
 
-  /* save localized id before adding language on it */
+  // Save localized id before adding language on it.
   metadata.localized_id = metadata.id;
 
-  /* if language */
+  // If language.
   if (language) {
     metadata.id = `${language}-${metadata.id}`;
   }
 
-  /* Determine order */
+  // Determine order.
   const id = metadata.localized_id;
   if (order[id]) {
     metadata.sidebar = order[id].sidebar;
@@ -172,5 +173,6 @@ module.exports = async function processMetadata(
       metadata.previous = (language ? `${language}-` : '') + order[id].previous;
     }
   }
+
   return metadata;
 };
diff --git a/v2/lib/load/docs/order.js b/v2/lib/load/docs/order.js
index 409a4049b9..83827954e8 100644
--- a/v2/lib/load/docs/order.js
+++ b/v2/lib/load/docs/order.js
@@ -5,8 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-// build the docs meta such as next, previous, category and sidebar
-
+// Build the docs meta such as next, previous, category and sidebar.
 module.exports = function createOrder(allSidebars = {}) {
   const order = {};
 
@@ -28,7 +27,7 @@ module.exports = function createOrder(allSidebars = {}) {
             break;
           case 'ref':
           case 'link':
-            // refs and links should not be shown in navigation
+            // Refs and links should not be shown in navigation.
             break;
           case 'doc':
             ids.push(item.id);
diff --git a/v2/lib/load/env.js b/v2/lib/load/env.js
index 4bcf87639e..aaaa7f01e0 100644
--- a/v2/lib/load/env.js
+++ b/v2/lib/load/env.js
@@ -11,7 +11,7 @@ const {idx} = require('./utils');
 const loadConfig = require('./config');
 
 module.exports = function loadEnv({siteDir, siteConfig}) {
-  // Translation
+  // Translation.
   const translation = {
     enabled: false,
     enabledLanguages: [],
@@ -23,31 +23,32 @@ module.exports = function loadEnv({siteDir, siteConfig}) {
   if (fs.existsSync(languagesFile)) {
     const languages = require(languagesFile); // eslint-disable-line
 
-    /* Enabled languages */
+    // Enabled languages.
     const enabledLanguages = languages.filter(lang => lang.enabled);
     if (!enabledLanguages || enabledLanguages.length === 0) {
       throw new Error(`Please at least enable one language in 'languages.js'`);
     }
     translation.enabledLanguages = enabledLanguages;
 
-    /* Default Language */
+    // Default language.
     const {defaultLanguage: defaultLanguageTag} = siteConfig;
     const defaultLanguage = enabledLanguages.find(
       lang => lang.tag === defaultLanguageTag,
     );
+
     if (!defaultLanguage) {
       throw new Error(
         `Please set a default language in ${
           loadConfig.configFileName
-        } which is enabled in 'languages.js'`,
+        } which is enabled in languages.js`,
       );
     }
-    translation.defaultLanguage = defaultLanguage;
 
+    translation.defaultLanguage = defaultLanguage;
     translation.enabled = true;
   }
 
-  // Versioning
+  // Versioning.
   const versioning = {
     enabled: false,
     latestVersion: null,
diff --git a/v2/lib/load/index.js b/v2/lib/load/index.js
index 7b9068053b..973fed100c 100644
--- a/v2/lib/load/index.js
+++ b/v2/lib/load/index.js
@@ -16,18 +16,18 @@ const {generate} = require('./utils');
 const genRoutesConfig = require('./routes');
 
 module.exports = async function load(siteDir) {
-  // @tested - siteConfig
+  // Site Config - @tested
   const siteConfig = loadConfig.loadConfig(siteDir);
   await generate(
     loadConfig.configFileName,
     `export default ${JSON.stringify(siteConfig, null, 2)};`,
   );
 
-  // @tested - env
+  // Env - @tested
   const env = loadEnv({siteDir, siteConfig});
   await generate('env.js', `export default ${JSON.stringify(env, null, 2)};`);
 
-  // docs
+  // Docs
   const docsDir = path.resolve(siteDir, '..', siteConfig.customDocsPath);
   const {docsMetadatas, docsSidebars} = await loadDocs({
     siteDir,
@@ -44,7 +44,7 @@ module.exports = async function load(siteDir) {
     `export default ${JSON.stringify(docsSidebars, null, 2)};`,
   );
 
-  /* Create source to metadata mapping */
+  // Create source to metadata mapping.
   const sourceToMetadata = {};
   Object.values(docsMetadatas).forEach(
     ({source, version, permalink, language}) => {
@@ -56,7 +56,7 @@ module.exports = async function load(siteDir) {
     },
   );
 
-  // pages
+  // Pages.
   const pagesDir = path.resolve(siteDir, 'pages');
   const pagesMetadatas = await loadPages({pagesDir, env, siteConfig});
   await generate(
@@ -64,7 +64,7 @@ module.exports = async function load(siteDir) {
     `export default ${JSON.stringify(pagesMetadatas, null, 2)};`,
   );
 
-  // blog
+  // Blog.
   const blogDir = path.resolve(siteDir, 'blog');
   const blogMetadatas = await loadBlog({blogDir, env, siteConfig});
   await generate(
@@ -72,10 +72,10 @@ module.exports = async function load(siteDir) {
     `export default ${JSON.stringify(blogMetadatas, null, 2)};`,
   );
 
-  // resolve outDir
+  // Resolve outDir.
   const outDir = path.resolve(siteDir, 'build');
 
-  // resolve the theme
+  // Resolve theme.
   const themePath = loadTheme(siteDir);
 
   const {baseUrl} = siteConfig;
@@ -101,7 +101,7 @@ module.exports = async function load(siteDir) {
     translatedDir,
   };
 
-  // Generate React Router Config
+  // Generate React Router Config.
   const routesConfig = await genRoutesConfig(props);
   await generate('routes.js', routesConfig);
 
diff --git a/v2/lib/load/pages.js b/v2/lib/load/pages.js
index 52c1276751..6b7ccb69da 100644
--- a/v2/lib/load/pages.js
+++ b/v2/lib/load/pages.js
@@ -16,10 +16,10 @@ async function loadPages({pagesDir, env, siteConfig}) {
 
   const {baseUrl} = siteConfig;
 
-  /* Prepare metadata container */
+  // Prepare metadata container.
   const pagesMetadatas = [];
 
-  /* Translation */
+  // Translation.
   const translationEnabled = idx(env, ['translation', 'enabled']);
   const enabledLanguages =
     translationEnabled && idx(env, ['translation', 'enabledLanguages']);
@@ -33,7 +33,7 @@ async function loadPages({pagesDir, env, siteConfig}) {
       const pathName = encodePath(fileToPath(relativeSource));
       if (translationEnabled && enabledLangTags.length > 0) {
         enabledLangTags.forEach(langTag => {
-          /* default lang should also be available. E.g: /en/users and /users is the same */
+          // Default lang should also be available. E.g: /en/users and /users is the same.
           if (langTag === defaultLangTag) {
             pagesMetadatas.push({
               permalink: pathName.replace(/^\//, baseUrl),
@@ -49,9 +49,8 @@ async function loadPages({pagesDir, env, siteConfig}) {
           };
           pagesMetadatas.push(metadata);
         });
-
-        // for defaultLanguage
       } else {
+        // Default Language.
         const metadata = {
           permalink: pathName.replace(/^\//, baseUrl),
           source,
diff --git a/v2/lib/load/theme.js b/v2/lib/load/theme.js
index 96123f98ed..14d8ffa155 100644
--- a/v2/lib/load/theme.js
+++ b/v2/lib/load/theme.js
@@ -24,6 +24,7 @@ module.exports = function loadConfig(siteDir) {
     'Markdown',
     'Search',
   ];
+
   themeComponents.forEach(component => {
     if (!require.resolve(path.join(themePath, component))) {
       throw new Error(
diff --git a/v2/lib/webpack/client.js b/v2/lib/webpack/client.js
index 1c4b507707..69d9638ea6 100644
--- a/v2/lib/webpack/client.js
+++ b/v2/lib/webpack/client.js
@@ -17,7 +17,7 @@ module.exports = function createClientConfig(props) {
   const config = createBaseConfig(props);
   config.entry('main').add(path.resolve(__dirname, '../core/clientEntry.js'));
 
-  // remove/clean build folders before building bundles
+  // Remove/clean build folders before building bundles.
   const {outDir} = props;
   config
     .plugin('clean')
@@ -33,7 +33,7 @@ module.exports = function createClientConfig(props) {
       {filename: path.join(outDir, 'react-loadable.json')},
     ]);
 
-  // show compilation progress bar and build time
+  // Show compilation progress bar and build time.
   const isProd = process.env.NODE_ENV === 'production';
   config
     .plugin('niceLog')
diff --git a/v2/lib/webpack/loaders/markdown/index.js b/v2/lib/webpack/loaders/markdown/index.js
index 49d33a294b..8b34fcea90 100644
--- a/v2/lib/webpack/loaders/markdown/index.js
+++ b/v2/lib/webpack/loaders/markdown/index.js
@@ -26,10 +26,10 @@ module.exports = function(fileString) {
     sourceToMetadata,
   } = options;
 
-  /* Extract content of markdown (without frontmatter) */
+  // Extract content of markdown (without frontmatter).
   const {body} = fm(fileString);
 
-  /* Determine the source dir. e.g: /docs, /website/versioned_docs/version-1.0.0 */
+  // Determine the source dir. e.g: /docs, /website/versioned_docs/version-1.0.0
   let sourceDir;
   const thisSource = this.resourcePath;
   if (thisSource.startsWith(translatedDir)) {
@@ -48,7 +48,7 @@ module.exports = function(fileString) {
     sourceDir = docsDir;
   }
 
-  /* Replace internal markdown linking (except in fenced blocks) */
+  // Replace internal markdown linking (except in fenced blocks).
   let content = body;
   if (sourceDir) {
     let fencedBlock = false;
@@ -59,14 +59,13 @@ module.exports = function(fileString) {
       if (fencedBlock) return line;
 
       let modifiedLine = line;
-      /* Replace inline-style links or reference-style links e.g:
-        This is [Document 1](doc1.md) -> we replace this doc1.md with correct link
-        [doc1]: doc1.md -> we replace this doc1.md with correct link
-      */
+      // Replace inline-style links or reference-style links e.g:
+      // This is [Document 1](doc1.md) -> we replace this doc1.md with correct link
+      // [doc1]: doc1.md -> we replace this doc1.md with correct link
       const mdRegex = /(?:(?:\]\()|(?:\]:\s?))(?!https)([^'")\]\s>]+\.md)/g;
       let mdMatch = mdRegex.exec(modifiedLine);
       while (mdMatch !== null) {
-        /* Replace it to correct html link */
+        // Replace it to correct html link.
         const mdLink = mdMatch[1];
         const targetSource = `${sourceDir}/${mdLink}`;
         const {permalink} =
@@ -86,21 +85,21 @@ module.exports = function(fileString) {
   const md = new Remarkable({
     langPrefix: 'hljs css language-',
     highlight(str, rawLang) {
-      // Default language fallback
+      // Default language fallback.
       const defaultLang =
         siteConfig.highlight && siteConfig.highlight.defaultLang;
 
-      // No syntax highlighting
+      // No syntax highlighting.
       if (rawLang === 'text' || (!rawLang && !defaultLang)) {
         return escapeHtml(str);
       }
 
-      // User's own hljs function to register additional languages
+      // User's own hljs function to register additional languages.
       if (siteConfig.highlight && siteConfig.highlight.hljs) {
         siteConfig.highlight.hljs(hljs);
       }
 
-      // Syntax highlighting
+      // Syntax highlighting.
       const lang = rawLang.toLowerCase() || defaultLang;
       try {
         if (hljs.getLanguage(lang)) {
@@ -119,10 +118,10 @@ module.exports = function(fileString) {
     linkify: true,
   });
 
-  // Register anchors plugin
+  // Register anchors plugin.
   md.use(anchors);
 
-  // Allow client sites to register their own plugins
+  // Allow client sites to register their own plugins.
   if (siteConfig.markdownPlugins) {
     siteConfig.markdownPlugins.forEach(plugin => {
       md.use(plugin);
@@ -134,7 +133,8 @@ module.exports = function(fileString) {
   const html = md
     .render(content)
     .replace(/<pre><code>/g, '<pre><code class="hljs">');
-  /* Return a React component */
+
+  // Return a React component.
   return `
 import React from 'react';
 import Markdown from '@theme/Markdown';
diff --git a/v2/lib/webpack/loaders/markdown/toSlug.js b/v2/lib/webpack/loaders/markdown/toSlug.js
index 832bf91759..01759d5790 100644
--- a/v2/lib/webpack/loaders/markdown/toSlug.js
+++ b/v2/lib/webpack/loaders/markdown/toSlug.js
@@ -59,7 +59,7 @@ module.exports = (string, context = {}) => {
   }
 
   if (typeof context.slugStats[slug] === 'number') {
-    // search for an index, that will not clash with an existing headings
+    // Search for an index, that will not clash with an existing headings
     while (
       typeof context.slugStats[`${slug}-${++context.slugStats[slug]}`] ===
       'number'
@@ -67,7 +67,7 @@ module.exports = (string, context = {}) => {
     slug += `-${context.slugStats[slug]}`;
   }
 
-  // we are tracking both original anchors and suffixed to avoid future name
+  // We are tracking both original anchors and suffixed to avoid future name
   // clashing with headings with numbers e.g. `#Foo 1` may clash with the second `#Foo`
   context.slugStats[slug] = 0;
 
diff --git a/v2/lib/webpack/server.js b/v2/lib/webpack/server.js
index d735dba4da..e4075efdf4 100644
--- a/v2/lib/webpack/server.js
+++ b/v2/lib/webpack/server.js
@@ -23,7 +23,7 @@ module.exports = function createServerConfig(props) {
 
   const {siteConfig, blogMetadatas, docsMetadatas, pagesMetadatas} = props;
 
-  // static site generator webpack plugin
+  // Static site generator webpack plugin.
   const docsFlatMetadatas = Object.values(docsMetadatas);
   const paths = [...blogMetadatas, ...docsFlatMetadatas, ...pagesMetadatas].map(
     data => data.permalink,
@@ -38,7 +38,7 @@ module.exports = function createServerConfig(props) {
     },
   ]);
 
-  // show compilation progress bar
+  // Show compilation progress bar.
   const isProd = process.env.NODE_ENV === 'production';
   config
     .plugin('niceLog')
@@ -46,7 +46,7 @@ module.exports = function createServerConfig(props) {
       {name: 'Server', color: 'yellow', skipBuildTime: isProd},
     ]);
 
-  // user extended webpack-chain config
+  // User-extended webpack-chain config.
   applyChainWebpack(props.siteConfig.chainWebpack, config, true);
 
   return config;
diff --git a/v2/lib/webpack/utils.js b/v2/lib/webpack/utils.js
index f9f79f70d8..799ddae04e 100644
--- a/v2/lib/webpack/utils.js
+++ b/v2/lib/webpack/utils.js
@@ -7,7 +7,7 @@
 
 const merge = require('webpack-merge');
 
-// Modify the generated webpack config with normal webpack config
+// Modify the generated webpack config with normal webpack config.
 function applyConfigureWebpack(userConfig, config, isServer) {
   if (typeof userConfig === 'object') {
     return merge(config, userConfig);
@@ -21,7 +21,7 @@ function applyConfigureWebpack(userConfig, config, isServer) {
   return config;
 }
 
-// Modify the generated webpack config with webpack-chain API
+// Modify the generated webpack config with webpack-chain API.
 function applyChainWebpack(userChainWebpack, config, isServer) {
   if (userChainWebpack) {
     userChainWebpack(config, isServer);
diff --git a/v2/test/load/docs/index.test.js b/v2/test/load/docs/index.test.js
index a98b8c256c..5d5d8f6063 100644
--- a/v2/test/load/docs/index.test.js
+++ b/v2/test/load/docs/index.test.js
@@ -18,7 +18,7 @@ describe('loadDocs', () => {
     expect(docsMetadatas.hello).toEqual({
       category: 'Guides',
       id: 'hello',
-      language: undefined,
+      language: null,
       localized_id: 'hello',
       permalink: '/docs/hello',
       previous: 'foo/baz',
@@ -27,12 +27,12 @@ describe('loadDocs', () => {
       sidebar: 'docs',
       source: path.join(docsDir, 'hello.md'),
       title: 'Hello, World !',
-      version: undefined,
+      version: null,
     });
     expect(docsMetadatas['foo/bar']).toEqual({
       category: 'Test',
       id: 'foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'foo/bar',
       next: 'foo/baz',
       next_id: 'foo/baz',
@@ -41,7 +41,7 @@ describe('loadDocs', () => {
       sidebar: 'docs',
       source: path.join(docsDir, 'foo', 'bar.md'),
       title: 'Bar',
-      version: undefined,
+      version: null,
     });
   });
 
@@ -52,7 +52,7 @@ describe('loadDocs', () => {
     expect(docsMetadatas['version-1.0.0-foo/bar']).toEqual({
       category: 'Test',
       id: 'version-1.0.0-foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'version-1.0.0-foo/bar',
       next: 'version-1.0.0-foo/baz',
       next_id: 'version-1.0.0-foo/baz',
@@ -66,7 +66,7 @@ describe('loadDocs', () => {
     expect(docsMetadatas['foo/bar']).toEqual({
       category: 'Test',
       id: 'foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'foo/bar',
       next: 'foo/baz',
       next_id: 'foo/baz',
@@ -156,7 +156,7 @@ describe('loadDocs', () => {
       sidebar: 'docs',
       source: path.join(translatedDir, 'ko', 'foo', 'baz.md'),
       title: 'baz',
-      version: undefined,
+      version: null,
     });
     expect(docsMetadatas['en-foo/bar']).toEqual({
       category: 'Test',
@@ -170,7 +170,7 @@ describe('loadDocs', () => {
       sidebar: 'docs',
       source: path.join(docsDir, 'foo', 'bar.md'),
       title: 'Bar',
-      version: undefined,
+      version: null,
     });
   });
 });
diff --git a/v2/test/load/docs/metadata.test.js b/v2/test/load/docs/metadata.test.js
index 5ada4b7ada..fa20489b0b 100644
--- a/v2/test/load/docs/metadata.test.js
+++ b/v2/test/load/docs/metadata.test.js
@@ -20,21 +20,21 @@ describe('processMetadata', () => {
     const dataB = await processMetadata(sourceB, docsDir, env, {}, siteConfig);
     expect(dataA).toEqual({
       id: 'foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'foo/bar',
       permalink: '/docs/foo/bar',
       source: path.join(docsDir, sourceA),
       title: 'Bar',
-      version: undefined,
+      version: null,
     });
     expect(dataB).toEqual({
       id: 'hello',
-      language: undefined,
+      language: null,
       localized_id: 'hello',
       permalink: '/docs/hello',
       source: path.join(docsDir, sourceB),
       title: 'Hello, World !',
-      version: undefined,
+      version: null,
     });
   });
 
@@ -45,12 +45,12 @@ describe('processMetadata', () => {
     const data = await processMetadata(source, docsDir, env, {}, siteConfig);
     expect(data).toEqual({
       id: 'permalink',
-      language: undefined,
+      language: null,
       localized_id: 'permalink',
       permalink: '/docs/endiliey/permalink',
       source: path.join(docsDir, source),
       title: 'Permalink',
-      version: undefined,
+      version: null,
     });
   });
 
@@ -80,7 +80,7 @@ describe('processMetadata', () => {
     const dataD = await processMetadata(sourceD, docsDir, env, {}, siteConfig);
     expect(dataA).toEqual({
       id: 'version-1.0.0-foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'version-1.0.0-foo/bar',
       permalink: '/docs/1.0.0/foo/bar',
       source: path.join(versionedDir, sourceA),
@@ -89,7 +89,7 @@ describe('processMetadata', () => {
     });
     expect(dataB).toEqual({
       id: 'version-1.0.0-hello',
-      language: undefined,
+      language: null,
       localized_id: 'version-1.0.0-hello',
       permalink: '/docs/1.0.0/hello',
       source: path.join(versionedDir, sourceB),
@@ -98,7 +98,7 @@ describe('processMetadata', () => {
     });
     expect(dataC).toEqual({
       id: 'foo/bar',
-      language: undefined,
+      language: null,
       localized_id: 'foo/bar',
       permalink: '/docs/next/foo/bar',
       source: path.join(docsDir, sourceC),
@@ -107,7 +107,7 @@ describe('processMetadata', () => {
     });
     expect(dataD).toEqual({
       id: 'hello',
-      language: undefined,
+      language: null,
       localized_id: 'hello',
       permalink: '/docs/next/hello',
       source: path.join(docsDir, sourceD),
@@ -275,7 +275,7 @@ describe('processMetadata', () => {
       permalink: '/docs/ko/foo/bar',
       source: path.join(translatedDir, sourceA),
       title: 'Bar',
-      version: undefined,
+      version: null,
     });
     expect(dataB).toEqual({
       id: 'ko-hello',
@@ -284,7 +284,7 @@ describe('processMetadata', () => {
       permalink: '/docs/ko/hello',
       source: path.join(translatedDir, sourceB),
       title: 'Hello, World !',
-      version: undefined,
+      version: null,
     });
     expect(dataC).toEqual({
       id: 'en-foo/bar',
@@ -293,7 +293,7 @@ describe('processMetadata', () => {
       permalink: '/docs/en/foo/bar',
       source: path.join(docsDir, sourceC),
       title: 'Bar',
-      version: undefined,
+      version: null,
     });
     expect(dataD).toEqual({
       id: 'en-hello',
@@ -302,7 +302,7 @@ describe('processMetadata', () => {
       permalink: '/docs/en/hello',
       source: path.join(docsDir, sourceD),
       title: 'Hello, World !',
-      version: undefined,
+      version: null,
     });
   });
 });
diff --git a/v2/test/load/env.test.js b/v2/test/load/env.test.js
index 7505ec1968..656ddc94bc 100644
--- a/v2/test/load/env.test.js
+++ b/v2/test/load/env.test.js
@@ -100,7 +100,7 @@ describe('loadEnv', () => {
     expect(() => {
       loadEnv({siteDir, siteConfig});
     }).toThrowErrorMatchingInlineSnapshot(
-      `"Please set a default language in 'docusaurus.config.js' which is enabled in 'languages.js'"`,
+      `"Please set a default language in docusaurus.config.js which is enabled in languages.js"`,
     );
   });
 });