The economy has been breaking down in fits and starts for the last year. The yield curve inversion several months back should have been the wake-up call. The Fed intervention in the repo market at the end of last year should have cemented the consensus that recession and/or big financial troubles lie ahead. That doesn't seem to have happened.
On the other hand, the 30-year yield has been on a downward slope for the last 20 years:
Recent history has shown that negative-yielding long term sovereign debt is no longer out of the question. The 30-year treasury could eventually end up with a negative yield. There are ways to make money from this, many of which end badly.