Thanks all for the reply.
Finally, I have sorted out how to define the rule correctly and I can reject the ticket now if the user submit the ticket through email which will end up with empty help topic. The rejected ticket can be checked from the Admin Panel -> Dashboard -> System Logs.
However, I'm still having problem to send the canned response to the user after he/she submitting the ticket via email in order to inform he/she that the submitted ticket is rejected.
I have done the settings (Admin Panel -> Manage -> Ticket Filter) as follow:
For Target Channel, I choose for Emails option and Filter Actions, I checked for Reject Ticket and Reply-to Email. I have chosen one option for the Canned Response as well.
Did I miss out anything in order to send the canned response to user after he/she submitting the email? Thank you.