?:0: attempt to call upvalue '?' (a nil value)

Question

I can't seem to get rid of this error (' ?:0: attempt to call upvalue '?' (a nil value) ').  What is "?:0:" ?
Thanks in advance for any help!
script:
local LrApplication = import 'LrApplication'
local LrDialogs = import 'LrDialogs'
local LrFileUtils = import 'LrFileUtils'
local catalog = LrApplication.activeCatalog()
local LrTasks = import 'LrTasks'
    function searchNtag()
        local targPhotos = catalog.getAllPhotos()
        for _, photo in ipairs(targPhotos) do
            local status = photo:getPropertyForPlugin('com.jonathonlefaive.tagstatus', 'tagboolean')
            if status then
                if status == nil then
                    local location = photo:getRawMetadata('path')
                    if LrFileUtils.isDeletable(location) == true then
                        photo:setPropertyForPlugin('com.jonathonlefaive.tagstatus', 'tagboolean', false, 2)
                    else
                        photo:setPropertyForPlugin('com.jonathonlefaive.tagstatus', 'tagboolean', true, 2)
                    end
                end
            end
        end
    end
function task()
    catalog.withPrivateWriteAccessDo(searchNtag)
end
LrTasks.startAsyncTask(task)

Answer 1

You're welcome Jonathon,
And, here's my wild guess as to the meaning of the error message:
When you use a dot, the function is still being called, its just that the first argument is nil (the expected 'self' argument), and
- There are no symbols for it - thus the question mark instead of a name.
- The value is zero - thus the zero (nil == 0).
Summary: Not sure what an "upvalue" is, but it makes sense to me in this context that its referring to the missing 'self' argument.
Just a guess.
_R_