Seedless Avocados?

Today I ate an avocado by slicing it with a butter knife and eating it with a spoon. When I sliced the avocado, as I usually do, by cutting around the seed starting from the pointed end of the fruit and cutting all the way around it. While cutting I noticed that the knife was going pretty deep without any resistance. I thought that was interesting and when I finished and twisted the two halves apart I noticed that the seed was very small and hollow. Either it had dried out or it was just a bad seed. Or maybe it was genetically engineered to have a small seed. Has anybody seen a hollow seed that you can cut with a butter knife before? I know I've seen it in peaches and nectarines where you can cut the fruit and the seed is already cracked in half on the inside.