Cannot read property 'collection' of null

First of all, let me thank you for this wonderful library. I finally finished migrating away a tree implementation (2 level only) from react-sortable-tree to this library, and it's been a revelation!

Having said that, there is a very occasional exception happening with this stack trace:
https://sentry.io/share/issue/f56935f0904a46b99651022ca63791cd/

I cannot reproduce it, I only get it from Sentry.

// I guess isActive should be checked before getActive.

Start with the linked Sentry stack trace and trace the relevant code paths around the `isActive` and `getActive` references in the report. Reproduce or isolate the null case, then add a focused regression test and verify that the reported exception is prevented.

Written by the indexing model from the issue text.