Null Error : Input capture sample

[Harvalove]

**null error **
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Press key: f to start capturing
2. key Q which should appear
3. key G to stop capturing (should reproduce error)

Expected behavior

1. Press key: f to start capturing
2. Press key: Q, W, or E
3. Press key: G to stop capturing
4. Press key: I to apply what you already captured

Screenshots
If applicable, add screenshots to help explain your problem.

Message:  null
Type:  ConcurrentModificationException
Method:  ArrayList$Itr.checkForComodification()
Line:  ArrayList.java:1013

java.util.ConcurrentModificationException
	at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
	at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
	at com.almasb.fxgl.core@17+dev-SNAPSHOT/com.almasb.fxgl.input.Input.update(Input.kt:759)
	at com.almasb.fxgl.scene@17+dev-SNAPSHOT/com.almasb.fxgl.scene.Scene.update(Scene.kt:103)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.MainWindow$update$1.invoke(MainWindow.kt:115)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.MainWindow$update$1.invoke(MainWindow.kt:115)
	at com.almasb.fxgl.core@17+dev-SNAPSHOT/com.almasb.fxgl.core.fsm.StateMachine.runOnActiveStates(StateMachine.kt:69)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.MainWindow.update(MainWindow.kt:115)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.FXGLApplication$GameApplicationService.onUpdate(FXGLApplication.kt:426)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.Engine.loop(Engine.kt:134)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.Engine.access$loop(Engine.kt:24)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.Engine$loop$1.invoke(Engine.kt:28)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.Engine$loop$1.invoke(Engine.kt:28)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.LoopRunner.frame(LoopRunner.kt:103)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.LoopRunner.access$frame(LoopRunner.kt:23)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.LoopRunner$impl$2$1.onTick(LoopRunner.kt:57)
	at com.almasb.fxgl.all@17+dev-SNAPSHOT/com.almasb.fxgl.app.AnimationTimerLoop$timer$1.handle(LoopRunner.kt:137)
	at [email protected]/javafx.animation.AnimationTimer$AnimationTimerReceiver.lambda$handle$0(AnimationTimer.java:58)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at [email protected]/javafx.animation.AnimationTimer$AnimationTimerReceiver.handle(AnimationTimer.java:57)
	at [email protected]/com.sun.scenario.animation.AbstractPrimaryTimer.timePulseImpl(AbstractPrimaryTimer.java:356)
	at [email protected]/com.sun.scenario.animation.AbstractPrimaryTimer$MainLoop.run(AbstractPrimaryTimer.java:266)
	at [email protected]/com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:571)
	at [email protected]/com.sun.javafx.tk.quantum.QuantumToolkit.pulse(QuantumToolkit.java:555)
	at [email protected]/com.sun.javafx.tk.quantum.QuantumToolkit.pulseFromQueue(QuantumToolkit.java:548)
	at [email protected]/com.sun.javafx.tk.quantum.QuantumToolkit.lambda$runToolkit$11(QuantumToolkit.java:352)
	at [email protected]/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
	at [email protected]/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
	at [email protected]/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
	at java.base/java.lang.Thread.run(Thread.java:833)

Runtime info(please complete the following information):

• OS and version: [e.g. Windows 10 / MacOS Catalina / etc.]

Attach log associated with the bug (can be found in "logs/")

Additional context / possible fixes
Add any other context about the problem here.