Drinking tea on an empty stomach is not recommended because it can suppress the secretion of gastric juices and reduces bile and acid in the stomach.
When you lose that acid it make it hard for your body to digest food.
However I always drink a cup of warm tea in the morning after getting up while making my breakfast and I've never had any problems doing so.
If you want to drink some tea in the morning on an empty stomach then it's okay to do so.
It's just not recommended by doctors and other health professionals.