pass from RandomMotion to gravity with nexttext

I try to move text from RandomMotion to gravity usin nexttext librarie

like this:

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Selector selector;

selector = new Selector();

selector.add("RandomMotion", new RandomMotion());

AbstractAction gravity = new Gravity(0.12);

Behaviour gravityBehaviour = gravity.makeBehaviour();

selector.add("Gravity", gravityBehaviour); <-- bad code!!

how make this work??

thanks!!