Merge pull request #1284 from oxygen-dioxide/textbox-undo

Fix openutau crashing after pressing Ctrl+Z in lyric box twice and enter

OpenUtau/ViewModels/LyricBoxViewModel.cs

@@ -19,7 +19,7 @@ public class SuggestionItem {
         [Reactive] public UVoicePart? Part { get; set; }
         [Reactive] public LyricBoxNoteOrPhoneme? NoteOrPhoneme { get; set; }
         [Reactive] public bool IsVisible { get; set; }
-        [Reactive] public string Text { get; set; }
+        [Reactive] public string? Text { get; set; }
         [Reactive] public SuggestionItem? SelectedSuggestion { get; set; }
         [Reactive] public ObservableCollectionExtended<SuggestionItem> Suggestions { get; set; }
 
@@ -55,7 +55,7 @@ private void UpdateSuggestion() {
                 return;
             }
             var scheduler = TaskScheduler.FromCurrentSynchronizationContext();
-            Task.Run(() => singer.GetSuggestions(Text).Select(oto => new SuggestionItem() {
+            Task.Run(() => singer.GetSuggestions(Text ?? "").Select(oto => new SuggestionItem() {
                 Alias = oto.Alias,
                 Source = string.IsNullOrEmpty(oto.Set) ? singer.Id : $"{singer.Id} / {oto.Set}",
             }).Take(32).ToList()).ContinueWith(task => {
@@ -77,7 +77,7 @@ private void UpdateSuggestion() {
         }
 
         public void Commit() {
-            if (Part == null || NoteOrPhoneme == null) {
+            if (Part == null || NoteOrPhoneme == null || Text == null) {
                 return;
             }
             if (!IsAliasBox) {