Retrival issue in Fusion Charts

I am working on FusionCharts. My requirement is : I need to display stacked3d graph in that, when i am generating xml for stacked3d graph.. there might be chance for particlualr month data wont be available.

XML Format :

"<chart palette='2'  bgColor='F0EEEE'    yAxisName='Firewalls Count'  showborder='0'            showPercentInToolTip='0' showLegend='1' showValues='0' labelStep='1' labelDisplay='WRAP'   slantLabels='0' useRoundEdges='1' numDIVLines='4'legendPosition='BOTTOM' legendCaption='Firewalls Onboarding Statistics'>"+
"<categories>"+
"<category label='May-14'/>"+
"<category label='Apr-14'/>"+
"<category label='Mar-14'/>"+
"<category label='Feb-14'/>"+
"<category label='Jan-14'/>"+
"<category label='Dec-13'/>
</categories>"+
"<dataset  seriesName='Firewalls'>"+
 "<set value='14' />"+
 "<set value='9'  />"+
 "<set value='5'  />"+
 "<set value='6'  />"+
 "<set value='14' />"+
 "<set value='9'  />"+
 "</dataset>"+
 "<dataset  seriesName='OS'>"+
 "<set value='2' />"+
 "<set value='3' />"+
 "<set value='7' />"+
 "<set value='5' />"+
 "<set value='2' />"+
 "</dataset>"+
 "<dataset  seriesName='Databases'>"+
 "<set value='6'  />"+
 "<set value='14' />"+
 "<set value='5'  />"+
 "<set value='6'  />"+
 "<set value='14' />"+
 "<set value='9'  />"+
 "</dataset>"+
 "</chart>"

In above XML For dataset OS : one set is missing.(one months data is not available in DB) My condition is if suppose any perticular months record is not there in database then how can i pass null or 0 value in that.

pls kindly give your valuable comments. thanks,