error in example Transition Group

[paxarpp]

In example "Transition Group
Styled transitions can be used with TransitionGroup
Live example on Stackblitz"
there is an error:
in file index.js
25: items.push(Math.max(...items) + 1)
should be changed to:
items.push(items[0] ? Math.max(...items) + 1 : 1)