Bug - Invoke-AzCostManagementQuery cmdlet should handle null value in the response rows (#21180)

* Fix the issue for Invoke-AzCostManagementQuery cmdlet response might have null value in the response rows.

* Update Changelog.md

* Update Changelog.md

---------

Co-authored-by: Yabo Hu <[email protected]>

Author: hachi1030-Allen

src/CostManagement/Changelog.md

@@ -17,7 +17,9 @@
     * Overview of change #1
         - Additional information about change #1
 -->
+
 ## Upcoming Release
+* Fixed an error that values in row could be null when grouping by the value of TagKey in Invoke-AzCostManagementQuery cmdlet.
 
 ## Version 0.3.0
 * Upgraded Api version to 2021-10-01
@@ -27,4 +29,3 @@
 
 ## Version 0.1.0
 * First preview release for module Az.CostManagement
-

src/CostManagement/custom/Invoke-AzCostManagementQuery.ps1

@@ -265,7 +265,11 @@ function Invoke-AzCostManagementUsageQueryInternal {
     foreach ($Row in $ResponseContent.Properties.Rows) {
       $QueryRow = New-Object System.Collections.Generic.List[string]
       foreach ($Item in $Row) {
-        $QueryRow.Add($Item.ToString())
+        if ($null -eq $Item) {
+          $QueryRow.Add($Item)
+        } else {
+          $QueryRow.Add($Item.ToString())
+        }
       }
       $RowList.Add($QueryRow)
     }