If you have received any contributions, no matter how small, then you are no longer the sole author. All copyright holders must agree in order to relicense unl

If you have received any contributions, no matter how small, then you are no longer the sole author. All copyright holders must agree in order to relicense unless all such holders signed a contributor license agreement which signs over all rights to the original author, and as multiple contributions have been made. Every single contributor must be contacted, and they must all agree. (Also, of course note that relicensing does not invalidate previous licenses - if I have a copy from when it was under AGPL, then nothing will ever change that.)