iOS - Facebook pop framework - Repeat forever "shake" animation
<p>I'm using Facebook pop framework to perform some cool animations. I'm shaking a button in this way :</p>

<pre><code>let rotation = POPSpringAnimation.init(propertyNamed: kPOPLayerRotation)
rotation.springBounciness = 30
rotation.springSpeed = 20
rotation.velocity = 30.0
rotation.repeatForever = true

button.layer.pop_addAnimation(rotation, forKey: "rotation")
</code></pre>

<p>Despite of the <code>repeatForever</code> set to <code>true</code> the animation doesn't repeat. I noticed that if we have the <code>toValue</code> property set, the animation repeats. Am I doing something wrong?</p>