Excel 2007 - Workbooks Linked - Referenced Field is Blank - Chart as Blank

I have a master workbook which calls data from six other workbooks. These workbooks track workload over twelve months from six locations. The master workbook consolidates it and this is where I have my charts. If the "child" workbook has no values (i.e. no data for April yet), the master workbook shows a 0 and therefore a 0 on the chart. I do not want this zero charted, but I'm afraid to mess with the cells since they reference another workbook

For example, the cell value is ='\\XXX.XX.XXX.XXX\CLINOPS\Workload Stats\Working\[Dwyer Monthly Workload - Master File.xlsx]Pharmacy'!E5 which displays a "0"

Any ideas?