Get policy filter fix

Author: pragrawa

src/ResourceManager/RecoveryServices.Backup/Commands.RecoveryServices.Backup/Cmdlets/ProtectionPolicy/GetAzureRmRecoveryServicesBackupProtectionPolicy.cs

@@ -152,8 +152,9 @@ public override void ExecuteCmdlet()
                             break;
                     }
 
-                    var backupManagementTypeFilter = 
-                    ServiceClientHelpers.GetServiceClientBackupManagementType(serviceClientProviderType);
+                    var backupManagementTypeFilter = string.IsNullOrEmpty(serviceClientProviderType) ?
+                            default(ServiceClientModel.BackupManagementType) :
+                            serviceClientProviderType.ToEnum<ServiceClientModel.BackupManagementType>();
 
                     ODataQuery<ServiceClientModel.ProtectionPolicyQueryObject> queryParams
                     = new ODataQuery<ServiceClientModel.ProtectionPolicyQueryObject>(