if you get spammed with empty messages from a/some players, write to support about it, so they might write a warning to said person.
But apart from that, i would not call it a bug, that you can have "empty" text. And if people dont want to write anything, again that is theirs choice and not much you/we can do about it. And even more its only shown when you have your mouse over a person avatar so its not like we would see it constantly anyway.