idk if this is a issue with your mod or someone eleses also sorry for double posting if that isnt allowed

java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableCollection.removeIf(Unknown Source)
at me.ichun.mods.morph.common.morph.nbt.NbtHandler.removeEmptyCompoundTags(NbtHandler.java:226)
at me.ichun.mods.morph.common.morph.MorphHandler.createVariant(MorphHandler.java:345)
at me.ichun.mods.morph.common.mode.ClassicMode.handleMurderEvent(ClassicMode.java:28)
at me.ichun.mods.morph.common.morph.MorphHandler.handleMurderEvent(MorphHandler.java:181)
at me.ichun.mods.morph.common.core.EventHandlerServer.onLivingDeath(EventHandlerServer.java:84)
at net.minecraftforge.eventbus.ASMEventHandler_2278_EventHandlerServer_onLivingDeath_LivingDeathEvent.invoke(.dynamic)
at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:85)
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302)
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283)
at net.minecraftforge.common.ForgeHooks.onLivingDeath(ForgeHooks.java:360)
at net.minecraft.entity.LivingEntity.func_70645_a(LivingEntity.java:1183)
at net.minecraft.entity.LivingEntity.func_70097_a(LivingEntity.java:1059)
at net.minecraft.entity.passive.AnimalEntity.func_70097_a(AnimalEntity.java:73)
at net.minecraft.entity.player.PlayerEntity.func_71059_n(PlayerEntity.java:1100)
at net.minecraft.entity.player.ServerPlayerEntity.func_71059_n(ServerPlayerEntity.java:1292)
at net.minecraft.network.play.ServerPlayNetHandler.func_147340_a(ServerPlayNetHandler.java:1205)
at net.minecraft.network.play.client.CUseEntityPacket.func_148833_a(SourceFile:74)
at net.minecraft.network.play.client.CUseEntityPacket.func_148833_a(SourceFile:13)
at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21)
at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18)
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144)
at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23)
at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:734)
at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:159)
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118)
at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:717)
at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:711)
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103)
at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:696)
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:646)
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232)
at java.lang.Thread.run(Unknown Source)
[16:21:56] [Server thread/FATAL] [minecraft/ThreadTaskExecutor]: Error executing task on Server
java.lang.UnsupportedOperationException: null
at java.util.Collections$UnmodifiableCollection.removeIf(Unknown Source) ~[?:1.8.0_351] {}
at me.ichun.mods.morph.common.morph.nbt.NbtHandler.removeEmptyCompoundTags(NbtHandler.java:226) ~[morph:10.2.1] {re:classloading}
at me.ichun.mods.morph.common.morph.MorphHandler.createVariant(MorphHandler.java:345) ~[morph:10.2.1] {re:mixin,re:classloading}
at me.ichun.mods.morph.common.mode.ClassicMode.handleMurderEvent(ClassicMode.java:28) ~[morph:10.2.1] {re:classloading}
at me.ichun.mods.morph.common.morph.MorphHandler.handleMurderEvent(MorphHandler.java:181) ~[morph:10.2.1] {re:mixin,re:classloading}
at me.ichun.mods.morph.common.core.EventHandlerServer.onLivingDeath(EventHandlerServer.java:84) ~[morph:10.2.1] {re:classloading}
at net.minecraftforge.eventbus.ASMEventHandler_2278_EventHandlerServer_onLivingDeath_LivingDeathEvent.invoke(.dynamic) ~[?:?] {}
at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:85) ~[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.minecraftforge.common.ForgeHooks.onLivingDeath(ForgeHooks.java:360) ~[forge:?] {re:mixin,re:classloading,pl:mixin:APP:supermartijn642corelib.mixins.json:ForgeHooksMixin,pl:mixin:APP:bountifulbaubles-forge.mixins.json:MixinForgeHooks,pl:mixin:APP:morecfm.mixins.json:ForgeHooksMixin,pl:mixin:A}
at net.minecraft.entity.LivingEntity.func_70645_a(LivingEntity.java:1183) ~[?:?] {re:mixin,pl:accesstransformer:B,xf:fml:placebo:placeboshieldblock,xf:fml:apotheosis:apothshieldblock,xf:fml:apotheosis:apothpotiondmg,re:classloading,pl:accesstransformer:B,xf:fml:placebo:placeboshieldblock,xf:fml:apotheosis:apothshieldblock,xf:fml:apotheosis:apothpotiondmg,pl:mixin:APP:supplementaries.mixins.json:LivingEntityMixin,pl:mixin:APP:cavesandcliffs.mixins.json:common.entity.LivingEntityMixin,pl:mixin:APP:cavesandcliffs.mixins.json:core.accessor.LivingEntityAccessor,pl:mixin:APP:animalbikes.mixins.json:LivingEntityMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.LivingEntityAccessor,pl:mixin:APP:the_bumblezone.mixins.json:entities.LivingEntityMixin,pl:mixin:APP:bountifulbaubles.mixins.json:MixinLivingEntity,pl:mixin:APP:oreberriesreplanted.mixins.json:LivingEntityAccessor,pl:mixin:APP:modifiers.mixins.json:MixinLivingEntity,pl:mixin:APP:blue_skies.mixins.json:LivingEntityMixin,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:morph.mixins.json:LivingEntityInvokerMixin,pl:mixin:APP:morph.mixins.json:LivingEntityMixin,pl:mixin:APP:chaosawakens.mixins.json:LivingEntityMixin,pl:mixin:APP:ars_nouveau.mixins.json:ExpInvokerMixin,pl:mixin:APP:ars_nouveau.mixins.json:MixinLivingEntity,pl:mixin:APP:environmental.mixins.json:LivingEntityMixin,pl:mixin:APP:upgrade_aquatic.mixins.json:LivingEntityMixin,pl:mixin:APP:endergetic.mixins.json:LivingEntityMixin,pl:mixin:APP:obscure_api.mixins.json:LivingEntityMixin,pl:mixin:APP:enhancedcelestials.mixins.json:MixinLivingEntity,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorLivingEntity,pl:mixin:A}
at net.minecraft.entity.LivingEntity.func_70097_a(LivingEntity.java:1059) ~[?:?] {re:mixin,pl:accesstransformer:B,xf:fml:placebo:placeboshieldblock,xf:fml:apotheosis:apothshieldblock,xf:fml:apotheosis:apothpotiondmg,re:classloading,pl:accesstransformer:B,xf:fml:placebo:placeboshieldblock,xf:fml:apotheosis:apothshieldblock,xf:fml:apotheosis:apothpotiondmg,pl:mixin:APP:supplementaries.mixins.json:LivingEntityMixin,pl:mixin:APP:cavesandcliffs.mixins.json:common.entity.LivingEntityMixin,pl:mixin:APP:cavesandcliffs.mixins.json:core.accessor.LivingEntityAccessor,pl:mixin:APP:animalbikes.mixins.json:LivingEntityMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.LivingEntityAccessor,pl:mixin:APP:the_bumblezone.mixins.json:entities.LivingEntityMixin,pl:mixin:APP:bountifulbaubles.mixins.json:MixinLivingEntity,pl:mixin:APP:oreberriesreplanted.mixins.json:LivingEntityAccessor,pl:mixin:APP:modifiers.mixins.json:MixinLivingEntity,pl:mixin:APP:blue_skies.mixins.json:LivingEntityMixin,pl:mixin:APP:citadel.mixins.json:LivingEntityMixin,pl:mixin:APP:morph.mixins.json:LivingEntityInvokerMixin,pl:mixin:APP:morph.mixins.json:LivingEntityMixin,pl:mixin:APP:chaosawakens.mixins.json:LivingEntityMixin,pl:mixin:APP:ars_nouveau.mixins.json:ExpInvokerMixin,pl:mixin:APP:ars_nouveau.mixins.json:MixinLivingEntity,pl:mixin:APP:environmental.mixins.json:LivingEntityMixin,pl:mixin:APP:upgrade_aquatic.mixins.json:LivingEntityMixin,pl:mixin:APP:endergetic.mixins.json:LivingEntityMixin,pl:mixin:APP:obscure_api.mixins.json:LivingEntityMixin,pl:mixin:APP:enhancedcelestials.mixins.json:MixinLivingEntity,pl:mixin:APP:assets/botania/botania.mixins.json:AccessorLivingEntity,pl:mixin:A}
at net.minecraft.entity.passive.AnimalEntity.func_70097_a(AnimalEntity.java:73) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:byg.mixins.json:common.entity.MixinAnimalEntity,pl:mixin:A}
at net.minecraft.entity.player.PlayerEntity.func_71059_n(PlayerEntity.java:1100) ~[?:?] {re:computing_frames,pl:accesstransformer:B,re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:PlayerEntityMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.PlayerEntityMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.PlayerInteractsEntityMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldDamageMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.HoneyShieldDisableMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.PlayerDamagedMixin,pl:mixin:APP:the_bumblezone.mixins.json:items.PlayerDamageShieldInvoker,pl:mixin:APP:bountifulbaubles-forge.mixins.json:MixinPlayerEntity,pl:mixin:APP:bountifulbaubles.mixins.json:MixinPlayerEntity,pl:mixin:APP:blue_skies.mixins.json:PlayerEntityMixin,pl:mixin:APP:morph.mixins.json:PlayerEntityMixin,pl:mixin:APP:chaosawakens.mixins.json:PlayerEntityMixin,pl:mixin:APP:ars_nouveau.mixins.json:ElytraPlayerMixin,pl:mixin:APP:forge-mca.mixin.json:MixinPlayerEntity,pl:mixin:APP:environmental.mixins.json:PlayerEntityMixin,pl:mixin:APP:endergetic.mixins.json:PlayerEntityMixin,pl:mixin:APP:assets/botania/botania.mixins.json:MixinPlayerEntity,pl:mixin:A}
at net.minecraft.entity.player.ServerPlayerEntity.func_71059_n(ServerPlayerEntity.java:1292) ~[?:?] {re:computing_frames,pl:accesstransformer:B,re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:betterendforge.mixins.json:ServerPlayerEntityMixin,pl:mixin:APP:endergetic.mixins.json:ServerPlayerEntityMixin,pl:mixin:APP:securitycraft.mixins.json:camera.ServerPlayerEntityMixin,pl:mixin:A}
at net.minecraft.network.play.ServerPlayNetHandler.func_147340_a(ServerPlayNetHandler.java:1205) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:A}
at net.minecraft.network.play.client.CUseEntityPacket.func_148833_a(SourceFile:74) ~[?:?] {re:classloading}
at net.minecraft.network.play.client.CUseEntityPacket.func_148833_a(SourceFile:13) ~[?:?] {re:classloading}
at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) ~[?:?] {re:mixin,re:classloading}
at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18) ~[?:?] {re:classloading}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) ~[?:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) ~[?:?] {re:mixin,re:computing_frames,re:classloading}
at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:734) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:159) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) ~[?:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:717) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:711) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103) ~[?:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:696) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:646) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232) ~[?:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:modernfix-common.mixins.json:perf.reuse_datapacks.MinecraftServerMixin,pl:mixin:APP:modernfix-common.mixins.json:perf.dedicated_reload_executor.MinecraftServerMixin,pl:mixin:APP:betterendforge.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:APP:chunkpregen.mixins.json:common.server.MinecraftServerMixin,pl:mixin:APP:the_bumblezone.mixins.json:entities.MinecraftServerMixin,pl:mixin:APP:good_nights_sleep.mixins.json:MinecraftServerMixin,pl:mixin:APP:byg.mixins.json:server.MixinMinecraftServer,pl:mixin:APP:notenoughcrashes.mixins.json:client.MixinMinecraftServerClientOnly,pl:mixin:A}
at java.lang.Thread.run(Unknown Source) [?:1.8.0_351] {}