The answer to your question is largely dependent on whether you develop any discomfort when doing so. Drinking coffee in the morning has become a routine for many people. This is usually taken with breakfast although some may like to take their coffee on an empty stomach the moment they open their eyes.
There is some debate as to whether there is an ideal time to take coffee for the "optimal" effect to keep one awake. Some recommend taking coffee in the late morning or early afternoon for best effects. Various reasons have also been postulated to discourage coffee drinking in the morning. This includes an elevated cortisol level in the morning and excessive stimulation with caffeine.
Despite the above, there is little evidence to show drinking coffee in the morning on an empty stomach actually cause significant harm to our body. In fact, coffee drinking has been shown to benefit people with a fatty liver problem. If you have an existing gastric acid-related issue, you may want to cut down on your coffee intake overall. For those who swear by their morning dose of caffeine like I do, I suggest worrying less and just enjoy your drink.