Python Dissolve tool - How to define Statistic type?

I'm trying to dissolve a polygon shapefile using python.

I want to dissolve the polygons using the field "COUNTY" AND I want to sum the housing units (field HU00) per County.
I wrote this:

arcpy.Dissolve_management("co_blk00_PLA", "co_blk00_dissolve","COUNTY",["HU00","SUM"],"MULTI_PART")

The python window says there's no syntax errors, but when I try to run it the error is:

"untime error <class 'arcgisscripting.ExecuteError'>: ERROR 000487: Statistic method is empty"

So how do I define the statistic method? I've tried several things and nothing works. Help!