By default, the assignee field has an unassigned option, which is equivalent to making the field optional. If you went to check out field configuration, you would have realized that you could not make the assignee field required as there is no such option available.
In this recipe, we will look at how to disable the unassigned option, effectively making the assignee a required field.
You cannot disable the unassigned option if you have:
Issues that are currently using that option for the assignee field
Projects that have unassigned set as the default assignee