[Baertram]

First you should remove the exampleoptions.lua and the LibAddonMenu-2.0.txt from the libs folder.
No need for them as the library is called from the manifest txt of the addon.

Then:
In line 218 there is a variable "buttoN" which isn#t declared anywhere so it is nil and throws this error:

if profileValue ~= boolValue then
        checkboxControl:GetHandler("OnClicked")(checkboxControl, button)
    end

Try to change it to something like this and see if it works then:

if profileValue ~= boolValue then
        checkboxControl:GetHandler("OnClicked")(checkboxControl)
    end

Or try this:

if profileValue ~= boolValue then
        local cbOnClickedHandler = checkboxControl:GetHandler("OnClicked")
        cbOnClickedHandler(checkboxControl)
    end