`Get-AzSecurityAlert` fails with `Object reference not set to an instance of an object.`

### Description

Az.Security v1.6.0, `Get-AzSecurityDetails` errors with `Object reference not set to an instance of an object.`, even though it successfully gets objects from Azure RM. This happens for one specific subscription, so it doesn't always fail.

Calling the API directly and convert it from JSON works fine. Example:

```powershell
Invoke-AzRestMethod -Method 'Get' -Path ('/subscriptions/{0}/providers/Microsoft.Security/alerts?api-version=2022-01-01' -f (Get-AzContext).'Subscription'.'Id')
```

Maybe related to #23499?

### Issue script & Debug output

Too much sensitive info, don't want to include that here.

After debug shows the raw JSON reply from Azure RM, this is outputted:

```
DEBUG: 10:45:56 - [ConfigManager] Got nothing from [DisableErrorRecordsPersistence], Module = [], Cmdlet = []. Returning default value [False].
DEBUG: 10:45:56 - [ConfigManager] Got nothing from [EnableDataCollection], Module = [], Cmdlet = []. Returning default value [True].
Get-AzSecurityAlert: Object reference not set to an instance of an object.
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 7.4.1
PSEdition Core
GitCommitId 7.4.1
OS Microsoft Windows 10.0.22631
Platform Win32NT
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 2.16.0 Az.Accounts {Add-AzEnvironment, Clear-AzConfig, Clear-AzContext, Clear-AzDefault…}
Script 5.2.1 Az.KeyVault {Add-AzKeyVaultCertificate, Add-AzKeyVaultCertificateContact, Add-AzKeyVaultKey, Add-AzKeyVaultManagedStorageAccount…}
Script 6.16.0 Az.Resources {Export-AzResourceGroup, Export-AzTemplateSpec, Get-AzDenyAssignment, Get-AzDeployment…}
Script 1.6.0 Az.Security {Add-AzSecurityAdaptiveNetworkHardening, Add-AzSecuritySqlVulnerabilityAssessmentBaseline, Confirm-AzSecurityAutomation, Disable-AzIotS…
Script 1.1.3 Az.Tools.Predictor {Disable-AzPredictor, Enable-AzPredictor, Open-AzPredictorSurvey, Send-AzPredictorRating}
```

### Error output

```PowerShell
PS > Resolve-AzError -Last

HistoryId: 84

Message : Object reference not set to an instance of an object.
StackTrace : at System.Linq.Enumerable.SelectListIterator`2.Fill(ReadOnlySpan`1 source, Span`1 destination, Func`2 func)
at System.Linq.Enumerable.SelectListIterator`2.ToList()
at Microsoft.Azure.Commands.Security.Models.Alerts.PSSecurityAlertConverters.ConvertToPSType(Alert value)
at System.Linq.Enumerable.SelectEnumerableIterator`2.ToList()
at Microsoft.Azure.Commands.Security.Cmdlets.Alerts.GetAlerts.ExecuteCmdlet()
at Microsoft.WindowsAzure.Commands.Utilities.Common.AzurePSCmdlet.ProcessRecord()
Exception : System.NullReferenceException
InvocationInfo : {Get-AzSecurityAlert}
Line : Get-AzSecurityAlert -Debug
Position : At line:1 char:1
+ Get-AzSecurityAlert -Debug
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~
HistoryId : 84

PS >
```

Start with GetAlerts.ExecuteCmdlet and PSSecurityAlertConverters.ConvertToPSType(Alert value) from the reported stack trace, then inspect the raw Azure Resource Manager alert response for null fields. Reproduce with Get-AzSecurityAlert against an affected subscription and verify that alert conversion completes without the NullReferenceException.

Written by the indexing model from the issue text.