By default, the automatic zeros setting​​ is enabled​. Students are still able to submit work after receiving an automatic zero, and you can grade as normal. 

Steps on How to Disable Automatic Zeros 

1. Enter your course. 
2. Click on the Gradebook tab. 
3. Click on the Settings icon on the top right of the Gradebook. It is located under student preview. 
4. Scroll down to the Automatic Zeros section and click on the checkbox that says Assign automatic zeros for past work.
   
5. Now, make a selection: (1) Keep existing automatic zeros (2) Clear existing automatic zeros.
6. Click on Confirm when finished.