fix: classes function including empty strings

js/src/forum/components/Post.js

@@ -124,7 +124,10 @@ export default class Post extends Component {
    * @returns {string[]}
    */
   classes(existing) {
-    let classes = (existing || '').split(' ').concat(['Post']);
+    const classes = (existing || '')
+      .split(' ')
+      .filter((x) => x.trim() !== '')
+      .concat(['Post']);
 
     const user = this.attrs.post.user();
     const discussion = this.attrs.post.discussion();