attempt to call method 'FindFirstChild' (a nil value) ?

Output: Players.Player.PlayerGui.Catalog.LocalScript:15: attempt to call method 'FindFirstChild' (a nil value)

function UpdateItems()
    local x, y = 0, 0.2
removeOldOutOfTheWay(gui.Main.Items:GetChildren())
    local lo = gui.Parent.Parent.Character:GetChildren()
    for _, child in pairs(lo) do
    if child.className == "Hat" then
       local new = settings.Items:Clone()
        new.Position = UDim2.new(x, 0, y, 0)
        new.Text = child.Name
        x = x + 0.031
new.Parent = gui.Main.Items
local removed = gui.Main.Items:GetChildren()
    for i = 1,#removed do
        removed[i].MouseButton1Up:connect (function()
            lo:FindFirstChild(removed[i].Text):remove()
        end)
        end
      end
    end
end

local a = gui.Parent.Parent.Character
a.ChildAdded:connect( UpdateItems )
a.ChildRemoved:connect( UpdateItems )
UpdateItems()