Steps to reproduce:

1. Visit http://127.0.0.1:8080/wiki/1?mobileaction=stable#/talk
2. Click 'Add discussion'
3. Type a space (' ') in the 'Topic subject' field and something else in the 'Whats is on your mind?' field.
4. Click 'Save'
5. You'll see that your talk page is added but you cannot click on it because the subject is empty.

Expected:
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.