Help with duplicate item remover?

Im trying to make one but what is wrong with my code becuase whenever i get the sword from the sword giver it gives me 1 but when i take the sword out it gives me 2.

local tmpTable = {} -- store items names
02	 
03	 for I,v in pairs(player.Backpack:GetChildren()) do --  loop through all items found
04	 
05	    if  tmpTable [v.Name] ~= nil then -- checks if item exists in the list
06	 
07	        print("a duplicate has been found") -- found item e.g. a duplicate
08	 
09	 v:Destroy() -- deletes tool
10	 
11	    else
12	 
13	        tmpTable [v.Name]  = "a"  -- we don't need to use the value we are only using the key
14	 
15	        print("item added to list")
16	 
17	 
18	end