Well said Ell.
If you went out to buy a writing pad you would be disappointed if you got anything but blank pages.
I think the 'empty' content may, therefore, be placed upon your expectations of what it is you expect to find or what it is you want to find.
A room, no furniture, carpets, curtains or anything can be described as an 'empty room'. You look into the room through a window and wonder why it is empty, when the rest of the house is beautifully furnished. Why is this one room the one that is not inhabited or decorated. Perhaps, you think, something happened in this room - something terrible such as the death of a loved one, or something to make it so you cannot live in it, such as termites which ate through the floor support and it's ready to give way at any moment.
Upon looking through the window and giving thought to what was there (or what wasn't) you have created the content.
As far as books go, they all have content. The book you are reading just now may contain different things for you as they do to me, but we both see something in it, whether it is the joy of having read it or the disgust at having wasted your time. Nobody can read the book and feel nothing.
Mxx