You really need to talk to your diabetic team about this. It's true that if you are on a basal bolus regime then you should be able to just inject the bolus when you eat, but your team will be able to tell you if that is your regime. They should also be telling you how much to inject for the carbohydrates you are eating (in which case 0 carbs = 0 insulin) but the very fact that you are asking this question says that this may not be the case.
Please phone or email your team. Insulin is way too dangerous for folk on a forum to be allowed to recommend doses.