patch 8.2.2289: Vim9: 'cpo' can become empty Commit: https://github.com/vim/vim/commit/e5a2dc87fd9d63dfd0d9c379e363ee8b8c05b14c Author: Bram Moolenaar <Bram@vim.org> Date: Sun Jan 3 19:52:05 2021 +0100 patch 8.2.2289: Vim9: 'cpo' can become empty Problem: Vim9: 'cpo' can become empty. Solution: Use empty_option instead of an empty string. Update quickfix buffer after restoring 'cpo'. (closes #7608)