bug fix

src/engine/objects/NPC.java

@@ -876,9 +876,10 @@ public class NPC extends AbstractCharacter {
         // zone collection
 
         this.parentZone = ZoneManager.getZoneByUUID(this.parentZoneUUID);
+        if(this.parentZone != null) {
             this.parentZone.zoneNPCSet.remove(this);
             this.parentZone.zoneNPCSet.add(this);
-
+        }
         // Setup location for this NPC
 
         this.bindLoc = new Vector3fImmutable(this.statLat, this.statAlt, this.statLon);