Activator performance improvement

Shouldn't close the previous PR early. Turns out I did not have to change much of my design.

Pinging previous trackers
@pranavkm
@halter73 
@rynowak
@ipjohnson
@yishaigalatzer 
Is the new method needed? Why can't the other method be called but with a `null` argument? This can be done via an extension method if needed.