fix bugs

app/javascript/mastodon/features/status/index.js

@@ -151,8 +151,15 @@ const makeMapStateToProps = () => {
       ancestorsIds = getAncestorsIds(state, { id: status.get('in_reply_to_id') });
       const root_status = ancestorsIds.size? getStatus(state, {id: ancestorsIds.get(0)}) : status; //error is directly visit url of non-root detailedStatus, feature!
       rootAcct = root_status? root_status.getIn(['account', 'acct']) : -1;
-      descendantsIds = rootAcct == '0' ? state.getIn(['contexts', 'replies', status.get('id')]).reverse() : getDescendantsIds(state, { id: status.get('id') });
-      deep      = rootAcct == '0' ? ancestorsIds.size : null;
+      if(rootAcct == '0') {
+        descendantsIds = state.getIn(['contexts', 'replies', status.get('id')]);
+        if(descendantsIds)
+          descendantsIds = descendantsIds.reverse(); 
+      }
+      else {
+        descendantsIds = getDescendantsIds(state, { id: status.get('id') });
+      }
+      deep     = rootAcct == '0' ? ancestorsIds.size : null;
       treeData = rootAcct == '0' ? getTreeData(state, {id: status.get('id')}) : null;
     }