I would say its just a deformity which happened
during growth.
Is this only on the new/top leaves?
deformities can happen for various reasons
caused mainly from over fertilization(especially
nitrogen),
and genetics can always play a role as much in
cannabis then anything else.
I think I had this happen with one of my first plants
along with complete leaves of mostly stem.
The reason I say think is because I remember
the leaves of mostly stem more than holes
it was a while ago.
I agree with JohnnySocco on this one.
My advice would be to thoroughly check
the plant for insects and if you find none
think about what you could have done to
affect the growth.
I would still use some neem as a protective
measure hope that helps.
