Some weird issue with arguments and parameters?

local DebounceCreator = {}
local ParameterRequest = require(game.ServerStorage.Parameter)


DebounceCreator.Debounce = function(waitTime, f, argument)
    local executing = false
    return function()
        if not executing then
            executing = true
            if next(argument) ~= nil then
                argument = ParameterRequest:new(argument)
                f(argument:unpack())
            else
                f()
            end
            wait(waitTime)
            executing = false
        end
    end
end

No need to know what ParameterRequest does I think, I'm getting an error at

            if next(argument) ~= nil then
                argument = ParameterRequest:new(argument)
                f(argument:unpack())
            else
                f()
            end

however if I change it to:

            if next(argument) ~= nil then
                foo = ParameterRequest:new(argument)
                f(parameter:unpack())
            else
                f()
            end

For some reason changing the name of 'argument' to 'foo' makes the code work all of a sudden. Why is this so?