The Essay question type allows you to ask students to submit an attachment as well as or instead of a text response.

There are two relevant settings: 'allow attachments' and 'require attachments'.  The second suggests that one or more attachments will be required. But they aren't. You can submit an answer without attaching anything.

Steps to reproduce:

As an administrator, manager or teacher:

1. Create a quiz in a course
2. Give it a name, leave the other defaults as they are, and click "Save and display"
3. Click "Edit quiz"
4. From the drop-down menu on the right, choose "Add.." and select "A new question"
5. A modal dialogue appears. Choose "Essay" from the list of Question Types and click "Add"
6. Give the question a name and description
7. Expand "Response options" and ensure the following settings:

1. 1. Response format: No online text
   2. Allow attachments: 1
   3. Require attachments: 1
2. Click "Save changes"

As a student in that course:

1. Click the name of the quiz
2. Click "Attempt quiz now"
3. Don't upload anything
4. **Click "Finish attempt"
5. Click "Submit all and finish", and confirm in the modal

Expected result:

Clicking "Finish attempt" should warn you that you've not uploaded anything

Actual result:

You can submit an empty answer with no attachment.