UI issue in the "tree view" if directory called "notebooks" is in the path.

## Description

Getting a pesky warning in the "tree" view, if path to the directory includes "notebooks"(with that exact spelling).

## Reproduce

1. Create a path that includes "notebooks", and has sub-directories. ("http://localhost:8888/tree/test/notebooks/test")
2. Navigate to that path via UI tree view.
3. Click Refresh
4. Get a pesky warning:

```
File Load Error for test
Invalid response: 404 Not Found
```
5. Renaming directory "notebooks" to **LITERALLY ANYTHING** (including capitalising any of the letters) removes the issue.

## Expected behavior

No warning happens

No source file or test is named. First reproduce the warning in the tree view at /tree/test/notebooks/test, click Refresh, and inspect the request that returns 404. Done means a path containing a directory named exactly "notebooks" refreshes without a warning and still shows its subdirectories.

Written by the indexing model from the issue text.