Allow revert to "none" on grading company

If you accidentally had a grading company set when you imported items to your collection, or if you had something set as the default field, and you later want to correct it to the "none" option (as shown on the app) or blank/null (as shown on the website), those changes currently don't persist when you try to save the item. It says that it saves, but if you go back into the item afterward, it will still show a grading company on it. I'd love to see this fixed so that I can fix my 20 or so items that say they're graded by PSA but they're not graded at all, instead of having to remove them and re-add them.