Custom Report on Customer Satisfaction - How to ignore 0 or null scores

[Ken S]

I have a custom report based on average customer satisfaction rating. I have a series for each assignee. I'm trying to ignore the 0 scores or tickets where a rating wasn't selected.
In the series, I've tried "satisfaction != 0" and "satisfaction > 0", but the 0s keep showing up in the line graph. Is there a way to trim the tickets where a user didn't submit a rating or filter out the 0s? 

Any help is appreciated.