scenario:

After adding a new chart to an Excel worksheet (which already have an existing chart), viewxls macro unable to render the Excel file and the following error appear in the page:

Error rendering macro 'viewxls' : com.benryan.conversion.ConversionException: java.lang.NullPointerException

The following error appear in atlassian-confluence.logs:

2014-01-28 22:34:58,897 ERROR [http-8080-4] [xhtml.view.macro.ViewMacroMarshaller] marshal Exception executing macro: viewxls, with message: com.benryan.conversion.ConversionException: java.lang.NullPointerException

With a single chart in the worksheet, the viewxls macro is rendered just fine.

Working sample:

1. Attach report-before.xlsx
2. Result: viewxls macro can render the Excel file just fine and the single chart is displayed

Non-working sample:

1. Attach report-after.xlsx
2. Result: You'll get this error in Confluence page:

   Error rendering macro 'viewxls' : com.benryan.conversion.ConversionException: java.lang.NullPointerException
   

The difference was that there is a new chart added to the same worksheet where there is already an existing chart.

Things that we have tested (based on the sample Excel files):

1. To successfully display the second chart - the chart needs to be created on the same 'JUNIT in Build' worksheet where the data resides.
2. Strangely, when editing the Excel file using Open Office but not using MS Excel and moved the 'JUNIT in Build' data into 'Charts' worksheet, both charts can be displayed fine: