Specified file attach path must exist or be writable even if no sources are enabled

If I don't enable any sources, the module still expects an existing and/or writable attach path. I didn't want to use filefield_sources for this particular field. However, saving the form causes drupal to display the validation error:

"Specified file attach path must exist or be writable."

To avoid this error I had to delete the default value. Another option would have been to just disable and uninstall the module.