Grouping in Invoke-AzCostManagementQuery results in: You cannot call a method on a null-valued expression.

### Description

When using grouping in `Invoke-AzCostManagementQuery` and the value is no set the cmdlet fails with `You cannot call a method on a null-valued expression.`

seems to be related to https://stackoverflow.com/questions/75682940/azure-cmdlet-how-to-group-results-with-invoke-azcostmanagementquery

### Issue script & Debug output

```PowerShell

$aggregation = @{
totalCost = @{
name = "Cost"
function = "SUM"
}
}

$grouping = @(
@{
type = "TagKey"
name = "owner"
}
)

$Result = Invoke-AzCostManagementQuery `
-Scope "/providers/Microsoft.Management/managementgroups/xxxxxx" `
-Timeframe 'Custom' `
-TimePeriodFrom $StartDate `
-TimePeriodTo $EndDate `
-Type 'ActualCost' `
-DatasetGranularity "Monthly" `
-DatasetAggregation $aggregation `
-DatasetGrouping $grouping -Debug

DEBUG: 2:05:36 PM - [ConfigManager] Got nothing from [DisplaySecretsWarning], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 2:05:36 PM - [ConfigManager] Got nothing from [DisplaySecretsWarning], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 2:05:36 PM - InvokeAzRestMethodCommand begin processing with ParameterSet 'ByPath'.
DEBUG: 2:05:36 PM - using account id 'xxxx'...
DEBUG: 2:05:36 PM - [ConfigManager] Got nothing from [DisplayBreakingChangeWarning], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: [Common.Authentication]: Authenticating using Account: 'xxxx', environment: 'AzureCloud', tenant: 'xxxx'
DEBUG: 2:05:36 PM - [ConfigManager] Got nothing from [DisableInstanceDiscovery], Module = [], Cmdlet = []. Returning default value [False].
DEBUG: 2:05:36 PM - [ConfigManager] Got nothing from [EnableLoginByWam], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 2:05:36 PM - [SilentAuthenticator] Calling SharedTokenCacheCredential.GetTokenAsync - TenantId:'xxxx', Scopes:'https://management.core.windows.net//.default', AuthorityHost:'https://login.microsoftonline.com/', UserId:'xxxx'
DEBUG: SharedTokenCacheCredential.GetToken invoked. Scopes: [ https://management.core.windows.net//.default ] ParentRequestId:
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] IsLegacyAdalCacheEnabled: yes
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] [Region discovery] Not using a regional authority.
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] [Region discovery] Not using a regional authority.
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] IsLegacyAdalCacheEnabled: yes
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] IsLegacyAdalCacheEnabled: yes
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z] Found 1 cache accounts and 0 broker accounts
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z] Returning 1 accounts
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] MSAL MSAL.CoreCLR with assembly version '4.61.3.0'. CorrelationId(xxxx)
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] === AcquireTokenSilent Parameters ===
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] LoginHint provided: False
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] Account provided: True
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] ForceRefresh: False
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx]
=== Request Data ===
Authority Provided? - True
Scopes - https://management.core.windows.net//.default
Extra Query Params Keys (space separated) -
ApiId - AcquireTokenSilent
IsConfidentialClient - False
SendX5C - False
LoginHint ? False
IsBrokerConfigured - False
HomeAccountId - False
CorrelationId - xxxx
UserAssertion set: False
LongRunningOboCacheKey set: False
Region configured:

DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] === Token Acquisition (SilentRequest) started:
Scopes: https://management.core.windows.net//.default
Authority Host: login.microsoftonline.com
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] [Region discovery] Not using a regional authority.
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] Access token is not expired. Returning the found cache entry. [Current time (08/27/2024 12:05:36) - Expiration Time (08/27/2024 12:45:10 +00:00) - Extended Expiration Time (08/27/2024 12:45:10 +00:00)]
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] Returning access token found in cache. RefreshOn exists ? False
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] [Region discovery] Not using a regional authority.
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx]
=== Token Acquisition finished successfully:
DEBUG: False MSAL 4.61.3.0 MSAL.CoreCLR .NET 8.0.8 MacOS [2024-08-27 12:05:36Z - xxxx] AT expiration time: 8/27/2024 12:45:10 PM +00:00, scopes: https://management.core.windows.net//.default https://management.core.windows.net//user_impersonation. source: Cache
DEBUG: SharedTokenCacheCredential.GetToken succeeded. Scopes: [ https://management.core.windows.net//.default ] ParentRequestId: ExpiresOn: 2024-08-27T12:45:10.0000000+00:00
DEBUG: [Common.Authentication]: Received token with LoginType 'User', Tenant: 'xxxx', UserId: 'xxxx'
DEBUG: ============================ HTTP REQUEST ============================

HTTP Method:
POST

Absolute Uri:
https://management.azure.com/providers/Microsoft.Management/managementgroups/xxxxx/providers/Microsoft.CostManagement/query?api-version=2019-11-01

Headers:
Accept-Language : en-US
x-ms-client-request-id : xxxx

Body:
{
"timePeriod": {
"from": "2024-06-30T22:00:00Z",
"to": "2024-07-31T21:59:59Z"
},
"dataset": {
"granularity": "Monthly",
"aggregation": {
"totalCost": {
"name": "Cost",
"function": "SUM"
}
},
"grouping": [
{
"type": "TagKey",
"name": "owner"
}
]
},
"type": "ActualCost",
"timeframe": "Custom"
}

DEBUG: ============================ HTTP RESPONSE ============================

Status Code:
OK

Headers:
Cache-Control : no-cache
Pragma : no-cache
Vary : Accept-Encoding
session-id : xxxx
x-ms-request-id : xxxx
x-ms-correlation-request-id : xxxx
x-ms-client-request-id : xxxx
X-Powered-By : ASP.NET
x-ms-ratelimit-remaining-tenant-resource-requests: 99
x-ms-routing-request-id : SWITZERLANDNORTH:20240827T120539Z:xxxx
Strict-Transport-Security : max-age=31536000; includeSubDomains
X-Content-Type-Options : nosniff
X-Cache : CONFIG_NOCACHE
X-MSEdge-Ref : Ref A: 9693F0FD639046C29CBB6874D45F549B Ref B: FRA231050411029 Ref C: 2024-08-27T12:05:36Z
Date : Tue, 27 Aug 2024 12:05:38 GMT

Body:
{
"id": "providers/Microsoft.Management/managementGroups/xxxxx/providers/Microsoft.CostManagement/query/xxxxx",
"name": "xxxxx",
"type": "Microsoft.CostManagement/query",
"location": null,
"sku": null,
"eTag": null,
"properties": {
"nextLink": null,
"columns": [
{
"name": "Cost",
"type": "Number"
},
{
"name": "BillingMonth",
"type": "Datetime"
},
{
"name": "TagKey",
"type": "String"
},
{
"name": "TagValue",
"type": "String"
},
{
"name": "Currency",
"type": "String"
}
],
"rows": [
// ...
[
1.07208,
"2024-06-01T00:00:00",
"owner",
null,
"EUR"
],
// ...
]
}
}

DEBUG: 2:05:39 PM - [ConfigManager] Got nothing from [DisplaySecretsWarning], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 2:05:39 PM - [ConfigManager] Got nothing from [DisplayRegionIdentified], Module = [], Cmdlet = []. Returning default value [True].
DEBUG: 2:05:39 PM - [ConfigManager] Got [False] from [CheckForUpgrade], Module = [], Cmdlet = [].
DEBUG: 2:05:39 PM - InvokeAzRestMethodCommand end processing.

Line |
81 | $Result = Invoke-AzCostManagementQuery `
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| You cannot call a method on a null-valued expression.
```
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 7.4.5
PSEdition Core
GitCommitId 7.4.5
OS Darwin 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:30 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T6000
Platform Unix
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1
WSManStackVersion 3.0
```

### Module versions

```PowerShell
ModuleType Version PreRelease Name ExportedCommands
---------- ------- ---------- ---- ----------------
Script 3.0.3 Az.Accounts {Add-AzEnvironment, Clear-AzConfig, Clear-AzContext, Clear-AzDefault…}
Script 0.3.2 Az.CostManagement {Get-AzCostManagementExport, Get-AzCostManagementExportExecutionHistory, Invoke…
```

### Error output

```PowerShell
Message : You cannot call a method on a null-valued expression.
StackTrace : at System.Management.Automation.ExceptionHandlingOps.CheckActionPreference(FunctionContext funcContext, Exception exception)
at System.Management.Automation.Interpreter.ActionCallInstruction`2.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.EnterTryCatchFinallyInstruction.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.Interpreter.Run(InterpretedFrame frame)
at System.Management.Automation.Interpreter.LightLambda.RunVoid1[T0](T0 arg0)
at System.Management.Automation.PSScriptCmdlet.RunClause(Action`1 clause, Object dollarUnderbar, Object inputToProcess)
at System.Management.Automation.PSScriptCmdlet.DoProcessRecord()
at System.Management.Automation.CommandProcessor.ProcessRecord()
Exception : System.Management.Automation.RuntimeException
InvocationInfo : {}
Line : $QueryRow.Add($Item.ToString())

Position : At /Users/xxxx/.local/share/powershell/Modules/Az.CostManagement/0.3.2/CostManagement.Autorest/custom/Invoke-AzCostManagementQuer
y.ps1:268 char:9
+ $QueryRow.Add($Item.ToString())
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
HistoryId : 3
```
```