How can I fill the texture of a leaf like this? So, I want to make my own leaf textures for trees, but if I just make a PNG with transparent background it gets a weird white edge. So I found that usually they use this effect with an alpha mask to get rid of that issue.
I remember watching a tutorial on how could I do it time ago, but i don't remember the technique, the name of it neither the tutorial name.

Any ideas?

(Actually, I found other ways to fix the issue, but I want to be able to use this)

Edit: First of all, thanks for your answers, very useful, but doing some more investigation I found the name of the technique and many ways to do it. Actually, the technique is called "Edge Padding" or even "Edge dilate".
There is a compositing node called Inpaint that does exactly that: 



It can be found iin the compositing nodes add menu shift+a in the Filter section: