Countblank and ImportRange for Conditional Formatting Custom Function

So I am trying to set up a conditional formatting custom function that will highlight the cell in question if a certain range on another spreadsheet contains any blank cells up to the last row of that spreadsheet. Can I write this as a formula for conditional formatting? Any help would be appreciated, thank you.

I tried:

=IF(COUNTBLANK(IMPORTRANGE(Index!$C9,"report.csv!E:F")))>0