code: function(assetKey) {
          var oldEntry = oldAvailableLists[assetKey];
          if ( oldEntry === undefined || oldEntry.off === true ) { return; }
          var listURL = oldEntry.contentURL;
          if ( Array.isArray(listURL) ) {
              listURL = listURL[0];
          }
          var newEntry = {
              content: 'filters',
              contentURL: listURL,
              external: true,
              group: 'custom',
              submitter: 'user',
              title: oldEntry.title || ''
          };
          newAvailableLists[listURL] = newEntry;
          µb.assets.registerAssetSource(listURL, newEntry);
          importedListKeys.push(listURL);
          µb.userSettings.externalLists += '\n' + listURL;
          µb.userSettings.externalLists = µb.userSettings.externalLists.trim();
          vAPI.storage.set({ externalLists: µb.userSettings.externalLists });
          µb.saveSelectedFilterLists([ listURL ], true);
      }
docs: Convert a no longer existing stock list into an imported list.