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    Expert tip

    Take a look at this blog post on how to set up Grid2 https://goo.gl/rxzbE6. A user related (in the email group on the source) that using older selenium libs solves this exception.

java.lang.NullPointerException: data cannot be null	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:229)	at net.citizensnpcs.api.npc.SimpleMetadataStore.checkPrimitive(SimpleMetadataStore.java:15)	at net.citizensnpcs.api.npc.SimpleMetadataStore.setPersistent(SimpleMetadataStore.java:86)	at net.citizensnpcs.api.npc.AbstractNPC$1.setPersistent(AbstractNPC.java:65)	at net.citizensnpcs.npc.skin.Skin.setNPCSkinData(Skin.java:315)	at net.citizensnpcs.npc.skin.Skin.apply(Skin.java:106)	at net.citizensnpcs.npc.skin.SkinPacketTracker.updateViewer(SkinPacketTracker.java:218)	at net.citizensnpcs.npc.skin.SkinUpdateTracker$1.run(SkinUpdateTracker.java:338)	at org.bukkit.craftbukkit.v1_10_R1.scheduler.CraftTask.run(CraftTask.java:53)	at org.bukkit.craftbukkit.v1_10_R1.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:349)	at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:697)	at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:360)	at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:646)	at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:550)	at java.lang.Thread.run(Unknown Source)