data loader to remove data

Hi,

I need to blank out address data in certain fields on Account records and was hoping to use the Data Loader for this.  I have created a CSV file with the Row ID of each record to be modified, but my question is what do I need to put in the CSV file columns for each of the fields to be 'blanked-out'?  I tried loading file something like:

"Row ID","Primary Country",Primary City","Primary State"

AEQA-12345,,,    <- nothing between commas

and

AEQA-12345, , ,    <- a space between the commas

These did not work.

Any idea would be appreciated.

Thanks, Greg.