Do I have to install a bedroom door at my cost?

[Jess Berdei]

I leased a 4-bed, 2-bath to renters. At the time, the fourth bedroom had no door hung in the door frame. It has a closet, and two means of egress (another door at the back of the room opens to the garage).

Now, after a month of living in the space without mentioning the door, they want a door hung and they want me to pay for it. 

When we replied that they could hang the door at their cost and just make sure the home is returned to it's original condition at move-out, they got really insistent and declared to my secretary that they're "not having this argument" with her. 

I just want to make sure I'm not doing anything wrong if I refuse.