minor fix in ui and nas backup provider

Author: abh1sar

plugins/backup/nas/src/main/java/org/apache/cloudstack/backup/NASBackupProvider.java

@@ -392,7 +392,7 @@ public Map<VirtualMachine, Backup.Metric> getBackupMetrics(Long zoneId, List<Vir
 
     @Override
     public List<Backup.RestorePoint> listRestorePoints(VirtualMachine vm) {
-        return List.of();
+        return null;
     }
 
     @Override

ui/public/locales/en.json

@@ -1396,6 +1396,7 @@
 "label.max.migrations": "Max. migrations",
 "label.maxbackup": "Max. Backups",
 "label.maxbackupstorage": "Max. Backup Storage (GiB)",
+"label.maxbackups.to.retain": "Max. Backups to retain",
 "label.maxbucket": "Max. Buckets",
 "label.maxcpu": "Max. CPU cores",
 "label.maxcpunumber": "Max CPU cores",

ui/src/views/compute/backup/FormSchedule.vue

@@ -108,7 +108,7 @@
               <a-form-item :label="$t('label.keep')" name="maxbackups" ref="maxbackups">
                 <a-tooltip
                   placement="right"
-                  :title="$t('label.backup')">
+                  :title="$t('label.maxbackups.to.retain')">
                   <a-input-number
                     style="width: 100%"
                     v-model:value="form.maxbackups"