When the yellow square is on it's second back way app hangs up and throws exception:

java.lang.NullPointerException
at javafx.animation.SequentialTransition.impl_playTo(SequentialTransition.java:414)
at com.sun.scenario.animation.shared.InfiniteClipEnvelope.timePulse(InfiniteClipEnvelope.java:126)
at javafx.animation.Animation.impl_timePulse(Animation.java:952)
at com.sun.scenario.animation.shared.AnimationPulseReceiver.timePulse(AnimationPulseReceiver.java:96)
at com.sun.scenario.animation.AbstractMasterTimer.timePulseImpl(AbstractMasterTimer.java:364)
at com.sun.scenario.animation.AbstractMasterTimer$MainLoop.run(AbstractMasterTimer.java:288)
at com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:498)
at com.sun.javafx.tk.quantum.QuantumToolkit$11.run(QuantumToolkit.java:355)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)