Most sources list it as 0 or 1 calories. Additionally considering that caffeine may increase your RMR ("Resting Metabolic Rate") by 3% or more[0][1], if you want to be "precise" it may be more accurate to say that black coffee contains negative calories.
So how precise do you need it to be? 0, 1, <5, or -1, -5 calories? Or is this just pedantic nitpicking?
Calorie has a pretty specific definition. What makes you feel like the scientific definition doesn't work for you?