You need to edit the document at least once to see info on it.
How to fix:
You need to modify the active document at least once for Sparrow to be able to access information about it.
Sheets: modifying at least one cell
Docs: Add text to at least one page
Slides: Add text/shape to at least one slide
Once you've done this, you can simply refresh the add-on (using the 3 dots at the top right of the add-on) and it should work as expected.