Observed on the 16/4/20 via analytics for 1.15-1.42:

Stacktrace:
java.lang.NullPointerException at bassebombecraft.entity.EntityUtils.hasAttribute(EntityUtils.java:465) at bassebombecraft.operator.conditional..run(IfEntityAttributeIsDefined.java:51) at bassebombecraft.operator.Operators.run(Operators.java:242) at bassebombecraft.event.item.RespawnEventHandler.handleLivingDeathEvent(RespawnEventHandler.java:39) at net.minecraftforge.eventbus.ASMEventHandler_17_RespawnEventHandler_handleLivingDeathEvent_LivingDeathEvent.invoke(.dynamic) at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:80) at net.minecraftforge.eventbus.EventBus.post(EventBus.java:258) at net.minecraftforge.common.ForgeHooks.onLivingDeath(ForgeHooks.java:348) at net.minecraft.entity.LivingEntity.func_70645_a(LivingEntity.java:1077) at net.minecraft.entity.LivingEntity.func_70097_a(LivingEntity.java:954) at net.minecraft.entity.LivingEntity.func_174812_G(LivingEntity.java:220) at net.minecraft.command.impl.KillCommand.func_198519_a(SourceFile:32) at net.minecraft.command.impl.KillCommand.func_229810_a_(SourceFile:25) at net.minecraft.command.impl.KillCommand$$Lambda$3428/1677732082.run(Unknown Source) at com.mojang.brigadier.CommandDispatcher.execute(CommandDispatcher.java:262) at net.minecraft.command.Commands.func_197059_a(Commands.java:205) at net.minecraft.network.play.ServerPlayNetHandler.func_147361_d(ServerPlayNetHandler.java:990) at net.minecraft.network.play.ServerPlayNetHandler.func_147354_a(ServerPlayNetHandler.java:973) at net.minecraft.network.play.client.CChatMessagePacket.func_148833_a(SourceFile:36) at net.minecraft.network.play.client.CChatMessagePacket.func_148833_a(SourceFile:9) at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) at net.minecraft.network.PacketThreadUtil$$Lambda$4580/1396125446.run(Unknown Source) 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:729) at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:141) at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:712) at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:706) at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:103) at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:691) at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:639) at java.lang.Thread.run(Thread.java:745)

See #782 for the problem with version 1 of the operator framework. Could be solved by upgrading to version 2.