Question How to store player inventory to give it to a player later

So I'm making a register plugin and I wanna store a player inventory and clear it then when the player logs in it gives the items back to the player.
I did this but doesn't work..

HashMap<Player, ItemStack[]> ivvv = new HashMap<Player, ItemStack[]>();
ItemStack[] inven;

public void saveInventory(Player p){
inven = new ItemStack[p.getInventory().getSize()];
for(int i=0;i>=p.getInventory().getSize();i++){
inven = p.getInventory().getItem(i);
}
ivvv.put(p, inven);
p.getInventory().clear();
}

public void restoreInventory(Player p){
for(int i=0;i>=p.getInventory().getSize();i++){
p.getInventory().addItem(ivvv.get(p));
}
}

 

@L3N
http://docs.codelanx.com/Bukkit/1.8/org/bukkit/inventory/Inventory.html#getContents--
The above method will return an ItemStack[]. Put that into your HashMap, and bingo, you're done.

 

Cool but when I type p.getInventory().addItem(hashmapname.get(p));
it throws the exception that the item cannot be null...