Formula doesn't treat reference cell as blank when link pasted in reference cell

I have been attempting to set up my spreadsheet with links to another spreadsheet so any changes will update automatically.

I also want to have a time stamp in column Q when ever column L is updated.

I have used a circular reference so that the time won't update each time so have used the following formula:

=IF(L2<>"",IF(Q2="",NOW(),Q2),"")

This works perfectly if the cells in column L are blank and get updated manually, however when I paste links to the other spreadsheet in these cells, even though the linked cells are blank it still creates the time stamp. I assume this is because the formula doesn't see the cells as blank because they contain links?

Is there a way to get the formula to see the cells as blank?

Thanks in advance.

Thanks Bernie,

Unfortunately it still doesn't appear to see the cell as blank. Also, it wouldn't be practical to type in formulas all the time.