attempt to index a nil value? Need help please?

This script would work with leaderstats. However we switched to a datastore in order to save data (obviously). However, with the data store, it doesnt work. Instead the script shows this error:

attempt to index a nil value (LINE 4 & 15)

If you find a fix for this please help me. Been trying for 2 hours. Heres some information:

CurrentBackpack is a string value that is in the player. (EXAMPLE: game.Players.LocalPlayer:FindFirstChild("CurrentBackpack"))

CurrentBP.Value is just the string value of the Current Backpack. Examples are: SmallBackpack, MediumBackpack, Etc). In here it gets for example SmallBackpack and finds it in ReplicatedStorage to clone into the player

game.Players.PlayerAdded:connect(function(plr)
    plr.CharacterAdded:connect(function(character)
        local CurrentBP = plr:WaitForChild("CurrentBackpack")
        local FirstBp = game.ReplicatedStorage.GameObjects.Backpacks:FindFirstChild(CurrentBP.Value):Clone()
        print(FirstBp)
        FirstBp.Parent = character
        FirstBp.Name = "Backpack"       





        plr:WaitForChild("CurrentBackpack").Changed:connect(function(value)
            print(value)
            local NewBackpack = game.ReplicatedStorage.GameObjects.Backpacks:FindFirstChild(plr.CurrentBackpack.Value):Clone()
            character:FindFirstChild("Backpack"):Destroy()
            NewBackpack.Parent = character
            NewBackpack.Name = "Backpack"
        end)
    end)
end)