// this null pointer error appears to happens sometimes when u attempt to equip 1 hand right handed weapon
error handling client message [C] 14 UseItem
java.util.ConcurrentModificationException
        at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
        at java.util.AbstractList$Itr.next(Unknown Source)
        at net.sf.l2j.gameserver.model.Inventory.setPaperdollItem(Inventory.java:299)
        at net.sf.l2j.gameserver.model.Inventory.equipItem(Inventory.java:455)
        at net.sf.l2j.gameserver.model.Inventory.equipItemAndRecord(Inventory.java:392)
        at net.sf.l2j.gameserver.clientpackets.UseItem.runImpl(UseItem.java:77)
        at net.sf.l2j.gameserver.clientpackets.ClientBasePacket.run(ClientBasePacket.java:56)
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
        at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
        at java.util.concurrent.FutureTask.run(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

// from inventory.java, here is the code surrounding lines 299, 455 and 392
// comments beginning with "//--+" have been added as my notes and are not in the code originally

// 299:
L2ItemInstance setPaperdollItem(int slot, L2ItemInstance item)
	{
		L2ItemInstance old = _paperdoll[slot]; 
		if (old != item)
		{
			if (old != null)
			{
				_paperdoll[slot] = null;
				old.setLocation(getBaseLocation());
				old.setLastChange(L2ItemInstance.MODIFIED);
				int mask = 0;
				for (int i=0; i < PAPERDOLL_LRHAND; i++)
				{
					L2ItemInstance pi = _paperdoll[i]; 
					if (pi != null)
						mask |= pi.getItem().getItemMask(); 
				}
				_wearedMask = mask;
//--+ next line is 299. "PaperdollListener listener" is shown as having the following problem in eclipse:
//--+ Syntax error on token(s), misplaced contruct(s)
				for (PaperdollListener listener : _paperdollListeners) 
					listener.notifyUnequiped(slot, old);
				old.updateDatabase();
			}
			if (item != null)
			{
				_paperdoll[slot] = item;
				item.setLocation(getEquipLocation(), slot);
				item.setLastChange(L2ItemInstance.MODIFIED);
				_wearedMask |= item.getItem().getItemMask();
//--+ same error here on the paperdolllistener as above
				for (PaperdollListener listener : _paperdollListeners)
					listener.notifyEquiped(slot, item);
				item.updateDatabase();
			}
		}
		return old;
	}

//455:
//--+ no errors appear in the following code in eclipse
			case L2Item.SLOT_R_HAND:
			{
				if (_paperdoll[PAPERDOLL_LRHAND] != null)
				{
					setPaperdollItem(PAPERDOLL_LRHAND, null);
					setPaperdollItem(PAPERDOLL_LHAND, null);
					setPaperdollItem(PAPERDOLL_RHAND, null);
				}
				else
				{
//--+ 455 below
					setPaperdollItem(PAPERDOLL_RHAND, null);
				}
				
				setPaperdollItem(PAPERDOLL_RHAND, item);
				break;
			}

//392:
    public L2ItemInstance[] equipItemAndRecord(L2ItemInstance item)
    {
		Inventory.ChangeRecorder recorder = newRecorder(); 
		try
		{
//--+ 392 below
	       equipItem(item, true); 
		} finally {
			removePaperdollListener(recorder);
		}
		return recorder.getChangedItems();
    }