This is correct... There is not one documented case of transmission from an undetectable partner. This is not to say that it's impossible as there is no evidence that it is impossible, however despite several recent studies done to attempt to quantify the risks among MSM
, there is no evidence that conclusively proves that it is either, despite efforts to acquire such evidence.
So... With that being said, it is starting to become generally accepted to say that sex with someone who is undetectable is safe. Statistically, it's actually safer than having sex with a condom with a partner with a high viral load. Just sayin'... Let the facts speak for themselves and draw your own conclusion from what evidence does exist.