/mm eggs get Pirate_1 causes internal error

When I try to do /mm eggs get Pirate_1 it causes an interal error. But when I try to do /mm mob spawn Pirate_1, it works fine.

I'm using a plugin called BossSkin which allows me to use player skins without needing a player to have the skin currently for it to work. I know BossSkin isn't the cause because /mm mob spawn Pirate_1 worked, meaning it shouldn't be an issue with the skin.

There are no errors when I do /mm reload. But when I do /mm eggs get Pirate_1, it gives this error in...

/mm eggs get Pirate_1 causes internal error