We've had a crash on our server related to NuclearCraft with a mekanism pipe attempting to extract gas from it. Although the NPE occurred in Mekanism's GasRegistry I checked the source code and it could only occur if either a gas in the registry had a null name (unlikely) or null was being passed to it. I suspect that GasHelper.getGasFromFluid is creating the null that caused the crash.

We're using the Enigmatica 2 Expert pack with NuclearCraft 2.12e

Important Part:
java.lang.NullPointerException: Ticking block entity at mekanism.api.gas.GasRegistry.getGas(GasRegistry.java:111) at nc.util.GasHelper.getGasFromFluid(GasHelper.java:37) at nc.tile.internal.fluid.GasTileWrapper.drawGas(GasTileWrapper.java:38) at mekanism.common.tile.transmitter.TileEntityPressurizedTube.func_73660_a(TileEntityPressurizedTube.java:69) at net.minecraft.world.World.func_72939_s(World.java:1835) at net.minecraft.world.WorldServer.func_72939_s(WorldServer.java:613) at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:767) at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:397) at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) at java.lang.Thread.run(Thread.java:748)

Full crash report: https://pastebin.com/Mtt8nWkX

Thanks very much for pointing that out! You're probably right in saying it's getting passed a null name. Which gas were you trying to extract, and from which machine?