I just upgraded to the latest LibGDX nightly (previous version was Nov 2012), and I'm working to update all the things that have changed.
But this seems more like a LWJGL bug. That was one of the things recently changed -- an upgrade to LWJGL 2.9.0.
When I click anywhere and send my running game to the background, instead of staying alive and existing on the taskbar (like it used to, for many months of development!) now the game tries to reset. And although I'm carefully ensuring that the Asset manager isn't null, it's complaining on that very line "NullPointerException". I know that error well (who doesn't?) but I can't seem to fix it.
More importantly, I'd like to know why LWJGL suddenly wants to pause/resume a game just because it's been sent to the background, of a DESKTOP OS (LInux 32-bit, Linux Mint 13 in my case). For that matter, my game worked fine on Android (pause/resume) and all that. But that was before.
Has anyone else experienced this? It might have to do with the upgrade to LWJGL 2.9.0.
It is very similar to this complaint:http://lwjgl.org/forum/index.php?topic=4517.0
Only it's not just a keyboard issue. It's restarting the program, so that the resources, etc. get loaded again. Just like on Android when you pause/resume -- but that didn't used to happen on the desktop version.