If the 'Require that students accept the submission statement' setting for an assignment is set to Yes but the Submission statement in Assignment settings is empty, students are unable to submit the assignment. On the Confirm submission page, clicking the Continue button only refreshes the page and does not submit the assignment. 

Steps to reproduce:

1. Log in as admin
2. Create a new course
3. Add an assignment to the course. Set the following submission settings:
   1. Require students to click the submit button - YES
   2. Require that students accept the submission statement - YES
4. Create a test user and enrol them into the course
5. In the admin/settings.php?section=modsettingassign page set assign | submissionstatement as empty and save
6. Log in as the test user
7. Navigate to the assignment created in step 3, click Add submission,  upload a test file, then click Submit Assignment
8. You will then be directed to the Confirm submission page, clicking on Continue will only refresh the page and not submit the assignment.