What is "vacuously"

Usage examples of "vacuously".

Phil Boyce was studying one more overhead diagnostic screen as the patient in hand lay on the sickbay bed smiling vacuously and staring into space.

The face was vacuously grinning, and gripped a fuzed stick of dynamite in its teeth.

Driving between these gigs was part of remaining a real and true sandsucker, and although she loved the barren badlands and the sweeping vistas of silver sage, she understood how the daunting emptiness of the desert could leave you smiling as vacuously as a sock puppet, and set you to talking of death and peanuts to an imaginary friend.