Seemingly benign NPE from initializing InputSystem for a headless server

[Cervator]

What you were trying to do

Test stuff! Clear logs are happy logs

What actually happened

A NullPointerException got logged breaking the perfect zen moment of staring at the logs :-( Actually, not really new, been seeing this for months if not longer.

Chances are some code gets initialized that makes no sense in a headless situation. May also want to check the ModuleTestingEnvironment starting a test since it uses both a headless server and headless clients.

Need to find where it gets logged then see if it makes sense to do a test of the network mode or something to only attempt that initialization where it makes sense, trying a little detective work in case it does actually result in something undesirable.

How to reproduce

• Run a headless server, seemingly any config
• Look through the logging, notice NPE during startup (after discovering modules, before activating them)
• Observe the server still working just fine, so it doesn't seem to be very bad ..

Log snippet

20:27:10.450 [main] INFO  o.t.i18n.TranslationSystemImpl - Discovered engine:menu_ru
20:27:10.754 [main] INFO  o.terasology.engine.TerasologyEngine - Initialization completed in 12.24sec.
20:27:11.500 [main] ERROR o.t.engine.ComponentSystemManager - Failed to initialise system org.terasology.input.InputSystem@374b6e33
java.lang.NullPointerException: null
	at org.terasology.input.InputSystem.initialise(InputSystem.java:124)
	at org.terasology.engine.ComponentSystemManager.initialiseSystem(ComponentSystemManager.java:160)
	at org.terasology.engine.ComponentSystemManager.initialise(ComponentSystemManager.java:144)
	at org.terasology.engine.subsystem.headless.mode.StateHeadlessSetup.init(StateHeadlessSetup.java:104)
	at org.terasology.engine.TerasologyEngine.switchState(TerasologyEngine.java:550)
	at org.terasology.engine.TerasologyEngine.changeState(TerasologyEngine.java:533)
	at org.terasology.engine.TerasologyEngine.run(TerasologyEngine.java:399)
	at org.terasology.engine.Terasology.main(Terasology.java:145)
20:27:12.389 [main] WARN  o.t.engine.internal.TimeBase - Delta too great (13205), capping to 1000
20:27:12.400 [main] INFO  o.t.e.m.loadProcesses.RegisterMods - Activating module: engine:2.2.1-SNAPSHOT

[DarkWeird]

This is bad "Good First Issue".

I looked into this place....

You need remove or replace on stub: NuiManager/InputSystem in headless context.

NuiManager is used almost everywhere. (via CoreRegistry too)
Сlose your eyes to 1 NPE, easier than refactoring the entire engine and major systems

[Cervator]

Belatedly removed the GFI label. Also want to link this to #3819 since if we end up extracting NUI that might be "big enough" to where better stubbing the UI in headless may make sense.