Easy work-around -- Move a graphical image from your pictures folder to your home folder. Choose the image as your wallpaper. Move the image to your pictures folder. Now the wallpaper is set to "None."
hat worked excepting I move it home/userid folder as no permissions to move to home/. Also I had to reboot once I deleted the image.
By "your home folder," I meant your /home/your-user-id folder. I did not say, nor did I mean /home (without user-id). This was to be done totally within your home folder, that is in your /home/your-user-id.
Your /home/your-user-id has a folder named Pictures. If you put an image in your /home/your-user-id/Pictures and choose it as your wallpaper, and then if you move that image from your /home/your-user-id/Pictures folder to your /home/your-user-id folder, your wallpaper will be set to "None." A logout/login will apply this change.