error trying to spawn zombies

Exception while calling NextTick callback (NullReferenceException: Object reference not set to an instance of an object)

at PlayerInventory.Strip () [0x00000] in <bb8c566a420f442c982c04bfa383880a>:0

at Oxide.Plugins.ZombieRocks+<Spawnnpc>c__AnonStorey1.<>m__0 () [0x004a0] in <a87a27079e8445599db3c82b14a9e1cc>:0

at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <157a94ee66ab4a7991faecd1eb84be3b>:0


how to fix this? 

Same here... Any fix?

Replying to myself: 

BetterNPC plugin kills non-BetterNPC plugin NPC on monuments if that settings is enabled.

Change BetterNPC config to exclude Rock Zombies:

"List of Npc types that should not be deleted": [
    "11162132011012",
    "NpcRaider",
    "RandomRaider",
    "56485621526987",
    "Rock Zombie"
  ],

Changed Status from Pending to Closed