I just got the following crash. The popup window said to email or post the error to the forums, so here it is 
For context, what I was doing at the time was trying to create a blueprint. I'd just deleted one and was going to recreate it again (slightly modified). Was just playing in creative mode, building stuff. I haven't tried to see if it can be reliably reproduced.
Linux 4.4.0-131-generic Java: 1.8.0_131 amd64 0.9.3.3_39 -H:4096 -D:3072 (Steam)
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Error occurred during application-update (25)
java.lang.NullPointerException
at aB.c.a(SourceFile:209)
at aB.c.a(SourceFile:110)
at ac.c.c(SourceFile:63)
at av.a.c(SourceFile:1122)
at w.g.a(SourceFile:623)
at w.c.onAction(SourceFile:943)
at com.jme3.input.InputManager.invokeActions(InputManager.java:169)
at com.jme3.input.InputManager.onKeyEventQueued(InputManager.java:462)
at com.jme3.input.InputManager.processQueue(InputManager.java:855)
at com.jme3.input.InputManager.update(InputManager.java:907)
at commons.JIWApplication.update(SourceFile:313)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.runLoop(LwjglAbstractDisplay.java:151)
at com.jme3.system.lwjgl.LwjglDisplay.runLoop(LwjglDisplay.java:198)
at com.jme3.system.lwjgl.LwjglAbstractDisplay.run(LwjglAbstractDisplay.java:232)
at java.lang.Thread.run(Thread.java:748)
