See: #5068 in which I first reported this bug but was ignored since I said some words that mod devs don't like to hear...

Reproduced with Forge version 36.0.58 and ONLY AE2 installed. See below:

[20:15:52] [Server thread/ERROR] [ne.mi.ev.EventBus/EVENTBUS]: Exception caught during firing event: null
Index: 3
Listeners:
0: NORMAL
1: ASM: net.minecraftforge.common.ForgeInternalHandler@4aad0e00 onChunkUnload(Lnet/minecraftforge/event/world/ChunkEvent$Unload;)V
2: ASM: class net.minecraftforge.client.model.ModelDataManager onChunkUnload(Lnet/minecraftforge/event/world/ChunkEvent$Unload;)V
3: net.minecraftforge.eventbus.EventBus$$Lambda$2959/676752045@39922326
java.lang.NullPointerException
at appeng.hooks.TickHandler.onUnloadChunk(TickHandler.java:180)
at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247)
at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239)
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302)
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283)
at net.minecraft.world.server.ChunkManager.func_219185_a(ChunkManager.java:403)
at java.util.concurrent.CompletableFuture.uniAccept(Unknown Source)
at java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source)
at java.util.concurrent.CompletableFuture$Completion.run(Unknown Source)
at net.minecraft.world.server.ChunkManager.func_223155_b(ChunkManager.java:388)
at net.minecraft.world.server.ChunkManager.func_219204_a(ChunkManager.java:366)
at net.minecraft.world.server.ServerChunkProvider.func_217207_a(ServerChunkProvider.java:323)
at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:333)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:851)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:787)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:78)
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:642)
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232)
at java.lang.Thread.run(Unknown Source)

[20:15:52] [Server thread/ERROR] [minecraft/ChunkManager]: Failed to save chunk [-11, 58]
java.util.concurrent.CompletionException: java.lang.NullPointerException
at java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) ~[?:1.8.0_171] {}
at java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) ~[?:1.8.0_171] {}
at java.util.concurrent.CompletableFuture.uniAccept(Unknown Source) ~[?:1.8.0_171] {}
at java.util.concurrent.CompletableFuture$UniAccept.tryFire(Unknown Source) ~[?:1.8.0_171] {}
at java.util.concurrent.CompletableFuture$Completion.run(Unknown Source) ~[?:1.8.0_171] {}
at net.minecraft.world.server.ChunkManager.func_223155_b(ChunkManager.java:388) ~[?:?] {re:classloading}
at net.minecraft.world.server.ChunkManager.func_219204_a(ChunkManager.java:366) ~[?:?] {re:classloading}
at net.minecraft.world.server.ServerChunkProvider.func_217207_a(ServerChunkProvider.java:323) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:333) ~[?:?] {re:classloading}
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:851) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:787) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:78) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:642) ~[?:?] {re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232) ~[?:?] {re:classloading,pl:accesstransformer:B}
at java.lang.Thread.run(Unknown Source) [?:1.8.0_171] {}
Caused by: java.lang.NullPointerException
at appeng.hooks.TickHandler.onUnloadChunk(TickHandler.java:180) ~[?:8.3.0-alpha.2] {re:classloading}
at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-4.0.0.jar:?] {}
at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-4.0.0.jar:?] {}
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-4.0.0.jar:?] {}
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-4.0.0.jar:?] {}
at net.minecraft.world.server.ChunkManager.func_219185_a(ChunkManager.java:403) ~[?:?] {re:classloading}
... 13 more

Forced crash log:
https://pastebin.com/yLEUGr8Q

Originally posted by @zpprsprk in #5068 (comment)

Duplicate of #5069