auto save errors

[17:35:17 INFO]: [Slimefun] Auto-Saving Block Data... (Next Auto-Save: 10m)
[17:35:17 INFO]: [Slimefun] Saving Blocks for World "world" (361,205 Change(s) queued)
[17:35:18 ERROR]: [org.bukkit.configuration.serialization.ConfigurationSerialization] Could not call method 'public static org.bukkit.inventory.meta.ItemMeta org.bukkit.craftbukkit.v1_15_R1.inventory.CraftMetaItem$SerializableMeta.deserialize(java.util.Map) throws java.lang.Throwable' of class org.bukkit.craftbukkit.v1_15_R1.inventory.CraftMetaItem$SerializableMeta for deserialization
java.lang.NullPointerException: null