disable joystick to avoid exception :

17:12:22.259 [LWJGL Renderer Thread] ERROR com.jme3.app.Application - Uncaught exception thrown in Thread[LWJGL Renderer Thread,5,main]
java.lang.AssertionError: null
	at com.jme3.input.controls.JoyAxisTrigger.joyAxisHash(JoyAxisTrigger.java:52) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.input.controls.JoyAxisTrigger.triggerHashCode(JoyAxisTrigger.java:73) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.input.InputManager.addMapping(InputManager.java:561) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.input.DefaultJoystickAxis.assignAxis(DefaultJoystickAxis.java:75) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.input.FlyByCamera.mapJoystick(FlyByCamera.java:272) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.input.FlyByCamera.registerWithInput(FlyByCamera.java:245) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.app.FlyCamAppState.initialize(FlyCamAppState.java:75) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.app.state.AppStateManager.initializePending(AppStateManager.java:251) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.app.state.AppStateManager.update(AppStateManager.java:281) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.app.SimpleApplication.update(SimpleApplication.java:239) ~[jme3-core-3.0.10.jar:na]
	at com.jme3.system.lwjgl.LwjglAbstractDisplay.runLoop(LwjglAbstractDisplay.java:151) ~[jme3-lwjgl-3.0.10.jar:na]
	at com.jme3.system.lwjgl.LwjglDisplay.runLoop(LwjglDisplay.java:185) ~[jme3-lwjgl-3.0.10.jar:na]
	at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:228) ~[jme3-lwjgl-3.0.10.jar:na]
	at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_20]