[BUG] Server crash: NPE in LibVulpes TileFluidHatch.drain when AE2 Fluid Storage Bus updates

[UraraChiya]

Version of Advanced Rocketry

2.2.14

Have you verified this is an issue in the latest unstable build

• [] Y
• N
• [] N/A

Version of LibVulpes

0.5.7

Version of Minecraft

1.12.2

Does this occur without other mods installed

• [] Y
• N
• [] N/A

If Y, what is the MINIMUM set of mods required.

Crash report or log or visualVM (if applicable)

https://mclo.gs/bEQg12L

Description of the problem

The dedicated server crashes during the server tick loop with a NullPointerException in LibVulpes:

Cannot invoke "net.minecraftforge.fluids.FluidStack.isFluidEqual(net.minecraftforge.fluids.FluidStack)" because "resource" is null

Stack trace points to:

zmaster587.libVulpes.tile.multiblock.hatch.TileFluidHatch.drain(TileFluidHatch.java:114)
zmaster587.libVulpes.cap.FluidCapability.drain(FluidCapability.java:27)
appeng.fluids.parts.FluidHandlerAdapter$InventoryCache.update(FluidHandlerAdapter.java:198)
appeng.fluids.parts.PartFluidStorageBus.getInventoryWrapper(PartFluidStorageBus.java:372)
appeng.fluids.parts.PartFluidStorageBus.getInternalHandler(PartFluidStorageBus.java:421)
appeng.fluids.parts.PartFluidStorageBus.getCellArray(PartFluidStorageBus.java:491)
appeng.me.cache.GridStorageCache.addCellProvider(GridStorageCache.java:153)
appeng.me.cache.GridStorageCache.cellUpdate(GridStorageCache.java:205)

It appears that AE2's fluid storage bus is updating/scanning the LibVulpes fluid hatch and calls drain with a null FluidStack resource. Per Forge's IFluidHandler, drain(null, ...) is a valid way to query/drain any fluid. TileFluidHatch.drain does not handle a null resource and calls resource.isFluidEqual(...), causing the server crash.

Reproduction

1. Use Minecraft 1.12.2 with Advanced Rocketry 2.2.14 and LibVulpes 0.5.7.
2. Have Applied Energistics 2 / AE2 fluid integration installed, e.g. AE2 UEL v0.56.7 with fluid storage bus support.
3. Place an Advanced Rocketry / LibVulpes multiblock fluid hatch.
4. Connect an AE2 fluid storage bus to the fluid hatch.
5. Power/update the ME network, or let the network update the storage bus.
6. The server crashes in the tick loop with the above NPE.

Expected behavior

TileFluidHatch.drain should handle a null FluidStack resource safely, as expected by Forge's fluid handler API, or at least not crash the server.

Actual behavior

Server crashes due to NullPointerException in TileFluidHatch.drain.

Additional environment

• Modpack: Enigmatica 2- Expert - Extended, Version 1.87.1

[kaduvill]

This is a bug introduced in ae2uel 0.56.7 by ae2uel.

• This is partly the reason modpack: MBC uses 0.56.5.
• fix has been PRed many months ago (over a year now?), and merged recently.