entity crashes game

i recently made a geckolib model, and i gave it some special attacks. one of them, is like a ground slam that checks if the player is on the ground, and if so flings them up into the air. it works great, but if the entity does is when there isn't a player in the 20x20x20 detection range, it just crashes my game. someone please help. i'm almost completely sure it has to do with the null block thing