Fixed broken tests

Export-Excel.ps1

@@ -539,6 +539,9 @@
             )
             #The write-verbose commands have been commented out below - even if verbose is silenced they cause a significiant performance impact and if it's on they will cause a flood of messages.
             Switch ($CellValue) {
+                { $null -eq $_     } { 
+                    break
+                }
                 { $_ -is [DateTime]} {
                     # Save a date with one of Excel's built in formats format
                     $TargetCell.Value = $_

__tests__/Export-Excel.Tests.ps1

@@ -9,7 +9,7 @@ Describe ExportExcel {
         $path = "$env:TEMP\Test.xlsx"
         Remove-item -Path $path -ErrorAction SilentlyContinue
         #Test with a maximum of 100 processes for speed; export all properties, then export smaller subsets.
-        $processes = Get-Process | select-object -first 100 -Property * -excludeProperty  Parent
+        $processes = Get-Process | where {$_.StartTime} | Select-Object -first 100 -Property * -excludeProperty  Parent
         $propertyNames = $Processes[0].psobject.properties.name
         $rowcount = $Processes.Count
         $Processes | Export-Excel $path  #-show
@@ -135,7 +135,7 @@ Describe ExportExcel {
         it "Created the worksheet with the expected name, number of rows and number of columns     " {
             $ws.Name                                                    | Should     be "sheet1"
             $ws.Dimension.Columns                                       | Should     be  1
-            $ws.Dimension.Rows                                          | Should     be  12
+            $ws.Dimension.End.Row                                       | Should     be  12
         }
 
         it "Set the default style for the sheet as expected                                        " {