Handle entries not existing in providers during flattening op

lib/utils/entry_tree_item_flattening.dart

@@ -18,10 +18,15 @@ extension FlatteningExtensions on EntryTreeItem {
     final items = <FlattenedTreeItem>[];
 
     // TODO handle if entries aren't in manager
-    final entryForItem =
+    final entryForItemResult =
-        ref.read(timelineEntryManagerProvider(profile, id)).value;
+        ref.read(timelineEntryManagerProvider(profile, id));
+    final entryForItem = entryForItemResult.value;
+    if (entryForItemResult.isFailure) {
+      return [];
+    }
+
     final myEntry = FlattenedTreeItem(
-      timelineEntry: entryForItem,
+      timelineEntry: entryForItemResult.value,
       isMine: isMine,
       level: level,
     );
@@ -31,14 +36,25 @@ extension FlatteningExtensions on EntryTreeItem {
       return items;
     }
 
-    final sortedChildren = children.map((id) {
+    final sortedChildren = children
+        .map((id) {
+          final treeResult = ref.read(entryTreeManagerProvider(profile, id));
+          final entryResult =
+              ref.read(timelineEntryManagerProvider(profile, id));
+          if (treeResult.isFailure || entryResult.isFailure) {
+            return null;
+          }
           final tree = ref.read(entryTreeManagerProvider(profile, id)).value;
-      final entry = ref.read(timelineEntryManagerProvider(profile, id)).value;
+          final entry =
+              ref.read(timelineEntryManagerProvider(profile, id)).value;
           return _EntryTreeItemWithEntity(entry, tree);
-    }).toList();
+        })
+        .where((e) => e != null)
+        .toList();
     for (final child in sortedChildren) {
       int childLevel = level + 1;
-      if (child.entry.authorId == entryForItem.authorId && level != baseLevel) {
+      if (child!.entry.authorId == entryForItem.authorId &&
+          level != baseLevel) {
         childLevel = level;
       }