ReadScale default to null on Set-AzSqlDatabase (#15168)

Author: bradrich-msft

src/Sql/Sql.Test/ScenarioTests/ReadScaleCrudTests.ps1

@@ -60,6 +60,11 @@ function Test-GetDatabaseReadScale ($serverVersion = "12.0", $location = "Southe
 		$db1 = Get-AzSqlDatabase -ResourceGroupName $server.ResourceGroupname -ServerName $server.ServerName -DatabaseName $db.DatabaseName
 		Assert-AreEqual Enabled $db1.ReadScale
 
+		# Alter database without specifying read scale value, it should remain enabled
+		$db2 = Set-AzSqlDatabase -ResourceGroupName $db.ResourceGroupName -ServerName $db.ServerName -DatabaseName $db.DatabaseName `
+			-RequestedServiceObjectiveName P2
+		Assert-AreEqual Enabled $db2.ReadScale
+
 		# Alter read scale properties, Premium ignores HighAvailabilityReplicaCount
 		$db2 = Set-AzSqlDatabase -ResourceGroupName $db.ResourceGroupName -ServerName $db.ServerName -DatabaseName $db.DatabaseName `
 			-ReadScale Disabled -HighAvailabilityReplicaCount -1