When supplying null "source" in an optionalClaim, the manifest results in an empty string and not null

[dammitjanet]

If a create an Application via the Azure Portal, the manifest shows the source as null

"optionalClaims": {
		"idToken": [
			{
				"name": "email",
				"source": null,
				"essential": false,
				"additionalProperties": []
			},
			{
				"name": "groups",
				"source": null,
				"essential": false,
				"additionalProperties": [
					"sam_account_name",
					"emit_as_roles"
				]
			}
		],

However if I create a optionalClaim via PowerShell, the resulting optionalClaim is string Empty and not null as provided.

	"optionalClaims": {
		"idToken": [
			{
				"name": "email",
				"source": "",
				"essential": false,
				"additionalProperties": []
			},
			{
				"name": "groups",
				"source": "",
				"essential": false,
				"additionalProperties": [
					"sam_account_name",
					"emit_as_roles"
				]
			}
		],

code to create the class instance in powershell is as follows, each of the instance uses the built in constructor and the 2nd parameter is the source, each is supplied as $null

$groups_claim = [Microsoft.Open.AzureAD.Model.OptionalClaim]::new("groups", $null, $false, @("sam_account_name","emit_as_roles"))
$email_claim = [Microsoft.Open.AzureAD.Model.OptionalClaim]::new("email", $null, $false, @())
$username_claim = [Microsoft.Open.AzureAD.Model.OptionalClaim]::new("preferred_username", $null, $false,  @())

$idtoken_claims = [System.Collections.Generic.List[Microsoft.Open.AzureAD.Model.OptionalClaim]]::new(2)
$idtoken_claims.Add($email_claim)
$idtoken_claims.Add($groups_claim)

$accessToken_claims = [System.Collections.Generic.List[Microsoft.Open.AzureAD.Model.OptionalClaim]]::new(2)
$accessToken_claims.Add($username_claim)
$accessToken_claims.Add($groups_claim)

$optional_claims = [Microsoft.Open.AzureAD.Model.OptionalClaims]::new($idtoken_claims, $accessToken_claims)

Set-AzureADApplication -ObjectId $appObjectId -RequiredResourceAccess $requiredResourcesAccess -OptionalClaims $optional_claims