Being a non-English native, I'm surprised when I read people who use a plural form when they're clearly talking about a single person.
Here are two excerpts from a software I used to work on, written by a former Irish co-worker:
... a supervisor must assign it to themselves and deal with it.
and:
This supervisor has no restaurants assigned to them.
I would have written the following sentences instead:
... a supervisor must assign it to himself and deal with it.
and:
This supervisor has no restaurants assigned to him.
Is the plural form correct English, and if so, is the plural preferred over the singular form?