How do I make a script that adds a shirt if a player dosent have one?

I need to have a script add a shirt if there is no shirt on the player because the script breaks when the player dosen't have a shirt.

Code It dosen't seem to add the shirt. Character is R15

local shirtid = 1453678633


game.Players.PlayerAdded:connect(function(plr)
    plr.CharacterAdded:connect(function(chr)
            local shirt = chr:FindFirstChild("Shirt")
                local nshirt = Instance.new("Shirt", chr)
                nshirt.Name = "Shirt"
                nshirt.ShirtTemplate = "rbxassetid://" ..shirtid
            end