Q&A: Answer to question with empty body leads to changing topic's title

Preconditions: user should have ADD_POST permission; QnA topic is created.

Steps to reproduce:

1. Open QnA topic with.
2. Click 'Answer to Question' button.
3. Leave the answer's body empty.
4. Click 'Answer to Question' button.

Actual result: topic's title is changed to

 ${htmlEscaper.process(${question.title})}
 

. See screenshot
Expected result: title isn't changed