Fix Highcharts column chart not rendering second series when first series is all zeros

[Copilot]

In a Highcharts column chart with multiple series, if the first series contains all-zero values, the second series fails to render correctly (shows flat columns). This is a Velocity 2.x truthiness bug: #if(0) evaluates to false, so every data point of the zero-valued series is silently dropped, producing an empty data: [] array that corrupts subsequent series rendering.

Proposed changes

Root cause: In column_chart.vm, the guard condition #if($row.get($serieColumnsMapped)) skips rows where the series value is 0 because Velocity 2.3 treats integer/double zero as falsy.

Fix: Move the #set before the #if and replace the falsy guard with a null-safe string check:

## Before (buggy — drops zero values)
#foreach($row in $rows)
    #if( $row.get($serieColumnsMapped))
        #set ($serieValue = $row.get($serieColumnsMapped))

## After (fixed — includes zeros, excludes only null/empty)
#foreach($row in $rows)
    #set ($serieValue = $row.get($serieColumnsMapped))
    #if("$!serieValue" != "")

"$!serieValue" uses Velocity's null-safe interpolation: outputs "" for null (excluded) and "0" for zero (included). Consistent with the pattern already used in scatter_chart.vm.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

The reverse case (first series non-zero, second series all-zero) already worked correctly — it only fails when the first series is all zeros, because the empty data array shifts Highcharts' internal series index alignment. The fix is a 2-line change with no behavioral impact on non-zero or null values.

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