[Compute] az vm auto-shutdown: Fix the issue that --webhook is required when --email is passed in (#18958)

* Fix the issue that --webhook is required when parameter --email is passed in

* resolve conflicts

Author: zhoxing-ms

src/azure-cli/azure/cli/command_modules/vm/custom.py

@@ -1065,15 +1065,16 @@ def auto_shutdown_vm(cmd, resource_group_name, vm_name, off=None, email=None, we
         raise CLIError('usage error: --time is a required parameter')
     daily_recurrence = {'time': time}
     notification_settings = None
-    if email and not webhook:
-        raise CLIError('usage error: --webhook is a required parameter when --email exists')
-    if webhook:
+    if email or webhook:
         notification_settings = {
-            'emailRecipient': email,
-            'webhookUrl': webhook,
             'timeInMinutes': 30,
             'status': 'Enabled'
         }
+        if email:
+            notification_settings['emailRecipient'] = email
+        if webhook:
+            notification_settings['webhookUrl'] = webhook
+
     schedule = Schedule(status='Enabled',
                         target_resource_id=vm_id,
                         daily_recurrence=daily_recurrence,