Cannot create a notebook if the folder name contains spaces

In Jupyter Notebook, I cannot create a notebook in a folder whose name contains spaces when I "go" to that folder directly.
It works well when I visit the tree root then navigate to that folder.

Steps to reproduce:

• create a folder with a space in the name (e.g. Untitled Folder);
• open that folder and copy the URL (e.g. ``);
• open a new tab and go to the copied URL directly;
• try to create a new notebook: it fails with the error No such directory: /Untitled%%20Folder.

It seems that the URL is encoded twice (notice the double "percent" symbol in the error message).

$ jupyter --version
jupyter core     : 4.6.3
jupyter-notebook : 6.1.4
qtconsole        : not installed
ipython          : 7.18.1
ipykernel        : 5.3.4
jupyter client   : 6.1.7
jupyter lab      : 2.2.8
nbconvert        : 6.0.7
ipywidgets       : 7.5.1
nbformat         : 5.0.8
traitlets        : 5.0.5

Start by reproducing the direct-URL workflow with a folder such as “Untitled Folder,” then compare it with navigating from the tree root. Trace the URL and path handling involved in notebook creation; done means creating a notebook directly in the space-containing folder succeeds without the path being double-encoded.