Fixed exception

Microsoft.Toolkit.Uwp.Notifications/Toasts/Builder/ToastContentBuilder.Actions.cs

@@ -112,7 +112,7 @@ namespace Microsoft.Toolkit.Uwp.Notifications
         /// <returns>The current instance of <see cref="ToastContentBuilder"/></returns>
         public ToastContentBuilder AddButton(IToastButton button)
         {
-            if (button is ToastButton toastButton && toastButton.Content == null)
+            if (button is ToastButton toastButton && toastButton.Content == null && toastButton.NeedsContent())
             {
                 throw new InvalidOperationException("Content is required on button.");
             }

Microsoft.Toolkit.Uwp.Notifications/Toasts/ToastButton.cs

@@ -25,6 +25,12 @@ namespace Microsoft.Toolkit.Uwp.Notifications
 
         private bool _usingDismissActivation;
 
+        internal bool NeedsContent()
+        {
+            // Snooze/dismiss buttons don't need content (the system will auto-add the localized strings).
+            return !_usingDismissActivation && !_usingSnoozeActivation;
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ToastButton"/> class.
         /// </summary>
@@ -428,11 +434,23 @@ namespace Microsoft.Toolkit.Uwp.Notifications
                 {
                     el.InputId = _snoozeSelectionBoxId;
                 }
+
+                // Content needs to be specified as empty for auto-generated Snooze content
+                if (el.Content == null)
+                {
+                    el.Content = string.Empty;
+                }
             }
             else if (_usingDismissActivation)
             {
                 el.ActivationType = Element_ToastActivationType.System;
                 el.Arguments = "dismiss";
+
+                // Content needs to be specified as empty for auto-generated Dismiss content
+                if (el.Content == null)
+                {
+                    el.Content = string.Empty;
+                }
             }
             else
             {

UnitTests/UnitTests.Notifications.Shared/Test_Toast_Xml.cs

@@ -980,7 +980,7 @@ namespace UnitTests.Notifications
         [TestMethod]
         public void Test_Toast_Xml_Actions_SnoozeAndDismissUsingBuilders()
         {
-            AssertActionsPayload("<actions><action activationType='system' arguments='snooze'/><action activationType='system' arguments='dismiss'/><action content='Hide' activationType='system' arguments='dismiss'/><action content='Later' activationType='system' arguments='snooze'/><action content='Remind me' activationType='system' arguments='snooze' hint-inputId='snoozePicker'/></actions>", new ToastActionsCustom()
+            AssertActionsPayload("<actions><action content='' activationType='system' arguments='snooze'/><action content='' activationType='system' arguments='dismiss'/><action content='Hide' activationType='system' arguments='dismiss'/><action content='Later' activationType='system' arguments='snooze'/><action content='Remind me' activationType='system' arguments='snooze' hint-inputId='snoozePicker'/></actions>", new ToastActionsCustom()
             {
                 Buttons =
                 {