I have found a possible bug in the AnimatedSprite.hx class of Spritesheet lib:
if I try to update a symbol that has no behaviour set it fails at line 133:
if (currentBehavior.loop) {
because currentBehavior is null.
I think it is necessary to put a precondition to execute the whole update function
public function update (deltaTime:Int):Void {
if (currentBehavior != null) {
[...]
}
}