Steps to reproduce:
- Visit http://127.0.0.1:8080/wiki/1?mobileaction=stable#/talk
- Click 'Add discussion'
- Type a space (' ') in the 'Topic subject' field and something else in the 'Whats is on your mind?' field.
- Click 'Save'
- You'll see that your talk page is added but you cannot click on it because the subject is empty.
When saving a discussion the backend (and front-end also?) should run a simple validation to check that the trimmed subject and discussion are not empty. This or some other validation check needs to run.
By the way, a similar validation should run when someone is replying to someone else's discussion.