Created by: tkrotoff
Edit: already done in #30597
Fix crash in dropdown: "Uncaught TypeError: Cannot read property 'focus' of undefined"
When opening the dropdown and pressing ArrowUp for the first time. Crash already present here: https://twbs-bootstrap.netlify.com/docs/4.3/components/dropdowns/
items.indexOf(event.target) || 0
gives -1 || 0
which returns... -1
... See explanations "Why are JavaScript negative numbers not always true or false?"