How to reproduce

1. Go to a subreddit that accepts text posts (such as this one)
2. Tap Submit Post and then Text
3. Tap on Text (optional)
4. Type something
5. Tap Post
6. A crash occurs

Possible fix

A way to fix this would be to show an alert when you try to make a post with an empty title.

Edit: I meant to say "Text post", not "Link post"