Should be able to do a filter for your Y axis value for greater than 0. This will only show items on the page that are greater than 0....
That doesn't seem to work. I suspect it has something to do with the source being an OLAP cube. If I copy the data and create a chart with the copied data it doesn't plot the missing values as zero. If I create the exact same chart using in Tableau 6.1 using the cube it doesn't plat the missing data either.
Hi.. Found an answer to this today as I was playing with my own dashboard that had the same effect after updating to 7.
I remember that they have added a new "feature" that fills in the missing values on certain measures... its actually a great feature for some of my data sets that use dates as it would not show 0 months and would skew averages and trend lines.
However in this case when you don't want it to fill them in, you can turn it off for a worksheet by going to Analysis -> Special Values -> Hide.