fix series header

Examples/Charts/MultiSeries1.ps1

@@ -9,7 +9,8 @@ A,B,C,Date
 $c = New-ExcelChart -Title Impressions `
     -ChartType Line -Header "Something" `
     -XRange "Impressions[Date]" `
-    -YRange @("Impressions[B]","Impressions[A]")
+    -YRange @("Impressions[B]","Impressions[A]") `
+    -SeriesHeader 'B data','A data'
 
 $data | 
     Export-Excel temp.xlsx -AutoSize -TableName Impressions -Show -ExcelChartDefinition $c

Export-Excel.ps1

@@ -362,11 +362,23 @@ function Export-Excel {
             $chartDefCount = @($chartDef.YRange).Count
             if($chartDefCount -eq 1) {
                 $Series=$chart.Series.Add($chartDef.YRange, $chartDef.XRange)
-                $Series.Header = $chartDef.Header
+                
+                $SeriesHeader=$chartDef.SeriesHeader
+                if(!$SeriesHeader) {$SeriesHeader="Series 1"}
+
+                $Series.Header = $SeriesHeader
             } else {
                 for($idx=0; $idx -lt $chartDefCount; $idx+=1) {
-                    $Series=$chart.Series.Add($chartDef.YRange[$idx], $chartDef.XRange)
-                    $Series.Header = $chartDef.Header[$idx]
+                    $Series=$chart.Series.Add($chartDef.YRange[$idx], $chartDef.XRange)                    
+
+                    if($chartDef.SeriesHeader.Count -gt 0) {
+                        $SeriesHeader=$chartDef.SeriesHeader[$idx]
+                    }
+                    
+                    if(!$SeriesHeader) {$SeriesHeader="Series $($idx)"}
+
+                    $Series.Header = $SeriesHeader
+                    $SeriesHeader=$null
                 }
             }
         }

New-ExcelChart.ps1

@@ -13,7 +13,8 @@ function New-ExcelChart {
         $ColumnOffSetPixels=5,
         [Switch]$NoLegend,
         [Switch]$ShowCategory,
-        [Switch]$ShowPercent
+        [Switch]$ShowPercent,
+        $SeriesHeader
     )
 
     [PSCustomObject]@{
@@ -31,5 +32,6 @@ function New-ExcelChart {
         NoLegend     = if($NoLegend)     {$true} else {$false}
         ShowCategory = if($ShowCategory) {$true} else {$false}
         ShowPercent  = if($ShowPercent)  {$true} else {$false}
+        SeriesHeader=$SeriesHeader
    }
 }