Board has javascript error, task can't be dragged

Problem/Motivation

It's not clear to me from the documentation how to move a task across columns on burndown/board/{name}. I think it should be possible to drag the task, since when I hover over the task it shows the grab cursor. However, I can't grab the task. Chrome browser console shows:

Uncaught ReferenceError: NULL is not defined
    at urlParam (burndown.board.js?v=9.5.9:188:24)
    at HTMLBodyElement.<anonymous> (burndown.board.js?v=9.5.9:13:23)
    at Function.each (jquery.min.js?v=3.6.3:2:3003)
    at E.fn.init.each (jquery.min.js?v=3.6.3:2:1481)
    at Object.attach (burndown.board.js?v=9.5.9:11:35)
    at drupal.js?v=9.5.9:24:24
    at Array.forEach (<anonymous>)
    at Drupal.attachBehaviors (drupal.js?v=9.5.9:21:34)
    at drupal.init.js?v=9.5.9:24:12
    at HTMLDocument.listener (drupal.init.js?v=9.5.9:14:7)

I also can't drag task up or down the board relative to other tasks.

Steps to reproduce

1. Install burndown.
2. Create a project
3. Add task to project backlog
4. Send task to board
4. Visit board