Game error on Helm of the host

When going to combat with [[Helm of the Host]] equipped onto an [[Undercover Operative]] which has copied another creature, the game shows the following error message.

> Game exception occurred: java.lang.ClassCastException: mage.game.permanent.token.EmptyToken cannot be cast to mage.game.permanent.Permanent
> Server version: 1.4.51-V4-beta3 (build: 2022-05-24 05:37)
> mage.cards.u.UndercoverOperativeApplier.apply(UndercoverOperative.java:59)
> mage.abilities.effects.common.CreateTokenCopyTargetEffect.apply(CreateTokenCopyTargetEffect.java:199)
> mage.cards.h.HelmOfTheHostEffect.apply(HelmOfTheHost.java:85)
> mage.abilities.AbilityImpl.resolveMode(AbilityImpl.java:201)
> mage.abilities.AbilityImpl.resolve(AbilityImpl.java:185)
> mage.abilities.TriggeredAbilityImpl.resolve(TriggeredAbilityImpl.java:149)
> mage.game.stack.StackAbility.resolve(StackAbility.java:89)
> mage.game.GameImpl.resolve(GameImpl.java:1646)
> mage.game.GameImpl.playPriority(GameImpl.java:1572)
> mage.game.turn.Step.priority(Step.java:61)
> mage.game.turn.Phase.playStep(Phase.java:184)
> mage.game.turn.Phase.play(Phase.java:89)
> mage.game.turn.Turn.play(Turn.java:132)
> mage.game.GameImpl.playTurn(GameImpl.java:1070)
> mage.game.GameImpl.play(GameImpl.java:980)
> mage.game.GameImpl.start(GameImpl.java:956)
> mage.server.game.GameWorker.call(GameWorker.java:34)
> java.util.concurrent.FutureTask.run(FutureTask.java:266)
> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
> java.lang.Thread.run(Thread.java:748)