Observed on the 31/8/21 via analytics for 1.16.5-2.2:

The error happened during attempt to respawn a CreeperEntity in RespawnEventHandler.handleLivingDeathEvent(..) in the Respawn2 operator.
Can be related to #1217.

Stack trace:
java.lang.NullPointerException at bassebombecraft.entity.EntityUtils.setAttribute(EntityUtils.java:456) at bassebombecraft.operator.entity.Respawn2.spawnEntity(Respawn2.java:95) at bassebombecraft.operator.entity.Respawn2.lambda$run$0(Respawn2.java:72) at bassebombecraft.operator.entity.Respawn2$$Lambda$16045/1316124243.accept(Unknown Source) at java.util.stream.Streams$RangeIntSpliterator.forEachRemaining(Streams.java:110) at java.util.stream.IntPipeline$Head.forEach(IntPipeline.java:557) at bassebombecraft.operator.entity.Respawn2.run(Respawn2.java:72) at bassebombecraft.operator.Operators2.run(Operators2.java:20) at bassebombecraft.operator.Operators2.run(Operators2.java:39) at bassebombecraft.operator.Sequence2.run(Sequence2.java:71) at bassebombecraft.operator.Operators2.run(Operators2.java:20) at bassebombecraft.operator.LazyInitOp2.run(LazyInitOp2.java:52) at bassebombecraft.operator.Operators2.run(Operators2.java:20) at bassebombecraft.event.item.RespawnEventHandler.handleLivingDeathEvent(RespawnEventHandler.java:51) at net.minecraftforge.eventbus.ASMEventHandler_324_RespawnEventHandler_handleLivingDeathEvent_LivingDeathEvent.invoke(.dynamic) at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:85) at net.minecraftforge.eventbus.EventBus$$Lambda$2545/573020748.invoke(Unknown Source) 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:374) 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.monster.MonsterEntity.func_70097_a(SourceFile:73) at net.minecraft.world.Explosion.func_77278_a(Explosion.java:199) at net.minecraft.world.server.ServerWorld.func_230546_a_(ServerWorld.java:1037) at net.minecraft.world.World.func_217385_a(World.java:566) at net.minecraft.entity.monster.CreeperEntity.func_146077_cc(CreeperEntity.java:222) at net.minecraft.entity.monster.CreeperEntity.func_70071_h_(CreeperEntity.java:146) at net.minecraft.world.server.ServerWorld.func_217479_a(ServerWorld.java:611) at net.minecraft.world.server.ServerWorld$$Lambda$14635/2105908668.accept(Unknown Source) at net.minecraft.world.World.func_217390_a(World.java:554) at net.minecraft.world.server.ServerWorld.func_72835_b(ServerWorld.java:404) at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:851) at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:787) at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:118) at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:642) at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232) at net.minecraft.server.MinecraftServer$$Lambda$14249/334402597.run(Unknown Source) at java.lang.Thread.run(Thread.java:745)