John Mastro <john.b.mastro@gmail.com> wrote:
> In commit 7e2a8b1, ibuffer.el was change to use `string-width' in a couple
> places where it previously used `length'. The result is that custom columns
> which can return nil, which worked in Emacs 25, will now cause an error.

I've attached a patch that fixes this. Rather than touching the calls to
`string-width' directly, it translates nil to the empty string. Either
way restores compatibility with Emacs 25, but translating nil to the
empty string seems preferable in that it saves later code from caring.

Even though it's a tiny change, I'm not a regular contributor or
particularly familiar with ibuffer's implementation, so any review is
appreciated. My copyright assignment is on file.

        John