Assignee of user input task

You can't have a task without an assignee. You can reassign the task to a user or a group of users. 

If you don't want to assign this task to someone, you just can assign it to an empty group.

Just curious if there are use cases wherein a developer wouldn't want to assign a task to anyone but an empty group ?

I really don't know the use case here or why he wants to remove the task assignee.
But a realistic scenario could be when you have a requirement where a user task can be worked by a certain group of people who are members of a specific group that is changing periodically (users constantly added to or removed from this group, maybe after LDAP sync). So one day it might have users and the other it might. The task will be assigned to the group without the system wondering whether there any are users in the group or not. 

I really don't know the use case here or why he wants to remove the task assignee.
But a realistic scenario could be when you have a requirement where a user task can be worked by a certain group of people who are members of a specific group that is changing periodically (users constantly added to or removed from this group, maybe after LDAP sync). So one day it might have users and the other it might. The task will be assigned to the group without the system wondering whether there any are users in the group or not.