diff --git a/src/node/utils/Minify.js b/src/node/utils/Minify.js
index 66a1926a9..8a97e5c32 100644
--- a/src/node/utils/Minify.js
+++ b/src/node/utils/Minify.js
@@ -53,6 +53,14 @@ const LIBRARY_WHITELIST = [
 // Rewrite tar to include modules with no extensions and proper rooted paths.
 const LIBRARY_PREFIX = 'ep_etherpad-lite/static/js';
 exports.tar = {};
+
+/**
+ * Prefix a path with `LIBRARY_PREFIX`
+ * If path starts with '$' it is not prefixed
+ *
+ * @param {string} path
+ * @returns {string} 
+ */
 const prefixLocalLibraryPath = (path) => {
   if (path.charAt(0) === '$') {
     return path.slice(1);
@@ -134,8 +142,7 @@ const requestURIs = (locations, method, headers, callback) => {
 
 /**
  * creates the minifed javascript for the given minified name
- * @param req the Express request
- * @param res the Express response
+ *
  */
 const minify = (req, res) => {
   let filename = req.params.filename;
@@ -349,6 +356,11 @@ const _requireLastModified = new Date();
 const requireLastModified = () => _requireLastModified.toUTCString();
 const requireDefinition = () => `var require = ${RequireKernel.kernelSource};\n`;
 
+/**
+ * @param {string} filename
+ * @param {string} contentType
+ * @param {Function} callback
+ */
 const getFileCompressed = (filename, contentType, callback) => {
   getFile(filename, (error, content) => {
     if (error || !content || !settings.minify) {
@@ -379,11 +391,11 @@ const getFileCompressed = (filename, contentType, callback) => {
           logger.info('Compress CSS file %s.', filename);
 
           content = await compressCSS(filename, ROOT_DIR);
+          callback(null, content.styles);
         } catch (error) {
           console.error(`CleanCSS.minify() returned an error on ${filename}: ${error}`);
+          callback(null, content)
         }
-
-        callback(null, content);
       });
     } else {
       callback(null, content);
diff --git a/src/node/utils/MinifyWorker.js b/src/node/utils/MinifyWorker.js
index c8bc09eb1..564fecb3b 100644
--- a/src/node/utils/MinifyWorker.js
+++ b/src/node/utils/MinifyWorker.js
@@ -7,56 +7,51 @@ const Terser = require('terser');
 const path = require('path');
 const Threads = require('threads');
 
+/**
+ * Returns content compressed with Terser
+ *
+ * @param {string} content javascript to be compressed
+ * @returns {MinifyOutput} compressed javascript
+ */
 function compressJS(content) {
   return Terser.minify(content);
 }
 
 function compressCSS(filename, ROOT_DIR) {
-  return new Promise((res, rej) => {
-    try {
-      const absPath = path.join(ROOT_DIR, filename);
+  const absPath = path.join(ROOT_DIR, filename);
 
-      /*
-       * Changes done to migrate CleanCSS 3.x -> 4.x:
-       *
-       * 1. Rework the rebase logic, because the API was simplified (but we have
-       *    less control now). See:
-       *    https://github.com/jakubpawlowicz/clean-css/blob/08f3a74925524d30bbe7ac450979de0a8a9e54b2/README.md#important-40-breaking-changes
-       *
-       *    EXAMPLE:
-       *        The URLs contained in a CSS file (including all the stylesheets
-       *        imported by it) residing on disk at:
-       *            /home/muxator/etherpad/src/static/css/pad.css
-       *
-       *        Will be rewritten rebasing them to:
-       *            /home/muxator/etherpad/src/static/css
-       *
-       * 2. CleanCSS.minify() can either receive a string containing the CSS, or
-       *    an array of strings. In that case each array element is interpreted as
-       *    an absolute local path from which the CSS file is read.
-       *
-       *    In version 4.x, CleanCSS API was simplified, eliminating the
-       *    relativeTo parameter, and thus we cannot use our already loaded
-       *    "content" argument, but we have to wrap the absolute path to the CSS
-       *    in an array and ask the library to read it by itself.
-       */
+ /*
+  * Changes done to migrate CleanCSS 3.x -> 4.x:
+  *
+  * 1. Rework the rebase logic, because the API was simplified (but we have
+  *    less control now). See:
+  *    https://github.com/jakubpawlowicz/clean-css/blob/08f3a74925524d30bbe7ac450979de0a8a9e54b2/README.md#important-40-breaking-changes
+  *
+  *    EXAMPLE:
+  *        The URLs contained in a CSS file (including all the stylesheets
+  *        imported by it) residing on disk at:
+  *            /home/muxator/etherpad/src/static/css/pad.css
+  *
+  *        Will be rewritten rebasing them to:
+  *            /home/muxator/etherpad/src/static/css
+  *
+  * 2. CleanCSS.minify() can either receive a string containing the CSS, or
+  *    an array of strings. In that case each array element is interpreted as
+  *    an absolute local path from which the CSS file is read.
+  *
+  *    In version 4.x, CleanCSS API was simplified, eliminating the
+  *    relativeTo parameter, and thus we cannot use our already loaded
+  *    "content" argument, but we have to wrap the absolute path to the CSS
+  *    in an array and ask the library to read it by itself.
+  */
 
-      const basePath = path.dirname(absPath);
+ const basePath = path.dirname(absPath);
 
-      new CleanCSS({
-        rebase: true,
-        rebaseTo: basePath,
-      }).minify([absPath], (errors, minified) => {
-        if (errors) return rej(errors);
-
-        return res(minified.styles);
-      });
-    } catch (error) {
-      // on error, just yield the un-minified original, but write a log message
-      console.error(`Unexpected error minifying ${filename} (${absPath}): ${error}`);
-      callback(null, content);
-    }
-  });
+ return new CleanCSS({
+   rebase: true,
+   rebaseTo: basePath,
+   returnPromise: true
+ }).minify([absPath])
 }
 
 Threads.expose({
diff --git a/src/node/utils/caching_middleware.js b/src/node/utils/caching_middleware.js
index 8bb3ab00d..98e239ca3 100644
--- a/src/node/utils/caching_middleware.js
+++ b/src/node/utils/caching_middleware.js
@@ -77,6 +77,9 @@ if (_crypto) {
   should replace this.
 */
 
+/**
+ * @class
+ */
 function CachingMiddleware() {
 }
 CachingMiddleware.prototype = new function () {