Detached HEAD appears in "git iswitch" output but cannot be selected

[openjck]

Steps to reproduce

1. git checkout HEAD~
2. git iswitch

Actual result

The selectable list of branches which can be selected includes the following:

(HEAD detached at [sha])

Selecting it prints:

fatal: invalid reference: (HEAD detached at [sha])

Expected result

This selectable list of branches does not include the following:

(HEAD detached at [sha])