Thx for the comments.
The addon we are talking about is
FCOItemSaver.
You are able to mark some items with icons and hide those items by filters, to prevent deconstruction/destroying/selling/trading of these items.
I'm trying to populate the information which item of the inventories was marked with which icon/filter to the dataEntry.data tree.
I know that the info must be added with the post-hook. Otherwise the data of the item isn't there and couldn't be used properly.
I'm doing it exactly the same like katkat42 within ResearchAssistant's method "AddResearchIndicatorToSlot" and I'm using the post-hook from the deconstruction oanel, and the normal inventory.
It is working fine, if I only add one entry (like ResearchAssistant does).
But I wanted to add an entry "FCO", another sub-entry "ItemSaver" and then an arry "Marked {}" with the information which mark has been set for the current item.
The current version of FCOItemSaver got 8 new entries "FCOItemSaverMarked1" to "FCOItemSaverMarked8", because the sub-entries and the array weren't working (always the error with nil).
If someone got the time to review the code, or test it for themselves: Please feel free to do so.
But it is not urgent! I've added some global functions to the addon so you are able to use them, instead of crawling the dataEntry.data trees.