conditional formatting that ignores 'blank' cells

Attached is a spreadsheet where I would like to highlight duplicates in column A of the first tab. However, A is used to rank people that sign up for an event so the unused cells all show up as duplicates. Is there a way to create an exception in conditional formatting that shows duplicates only in the cells that have actual ranks in them?

Any help is greatly appreciated!

You have to do it with a custom formula:

Formula:

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See attached.

Thanks for the quick reply!!

Works perfectly!!