There's no simple "one click" checkbox solution for that. But you can set up your Spreadsheet to do that.
You'll need a formula that will retrieve the content of your email (or part of the content), and this formula will filter out the blank answers.
Then you configure your FormEmailer to apply this formula automatically and use it as a placeholder for your email.
If you use html in your formula, you'll also need to use the "sHtml" formatting. Please check out the
Advanced settings page, specifically the "Formulas location" part, and the
Formatting page.
Regards,
Henrique G. Abreu