public AnimationMask getMask() {
        return mask;
    }
Retrieves the animation mask for this action.
The animation mask controls which part of the model would be animated. A model part can be
registered using a {@link com.jme3.anim.Joint}.

@return the animation mask instance, or null if this action will animate the entire model
@see com.jme3.anim.AnimLayer to adjust the animation mask to control which part will be animated
jme3-core/src/main/java/com/jme3/anim/tween/action/Action.java