Cannot invoke "com.sun.glass.ui.Timer.resume()" because "this.pulseTimer" is null

[hexmind]

Exception in thread "Thread-2" java.lang.NullPointerException: Cannot invoke "com.sun.glass.ui.Timer.resume()" because "this.pulseTimer" is null
	at com.sun.javafx.tk.quantum.QuantumToolkit.resumeTimer(QuantumToolkit.java:513)
	at com.sun.javafx.tk.quantum.QuantumToolkit$PulseTask.set(QuantumToolkit.java:204)
	at com.sun.javafx.tk.quantum.QuantumToolkit.setAnimationRunnable(QuantumToolkit.java:884)
	at com.sun.javafx.tk.quantum.MasterTimer.postUpdateAnimationRunnable(MasterTimer.java:105)
	at com.sun.scenario.animation.AbstractMasterTimer$MainLoop.updateAnimationRunnable(AbstractMasterTimer.java:324)
	at com.sun.scenario.animation.AbstractMasterTimer.addPulseReceiver(AbstractMasterTimer.java:176)
	at javafx.animation.Animation.addPulseReceiver(Animation.java:148)
	at javafx.animation.Animation.startReceiver(Animation.java:154)
	at javafx.animation.Animation.play(Animation.java:912)
	at org.graphstream.ui.fx_viewer.FxViewer.lambda$init$1(FxViewer.java:220)
	at java.base/java.lang.Thread.run(Thread.java:833)

gs-ui-javafx 2.0
openjdk-17.0.2