Exact URL of where the bug happened

https://lichess.org/training/dashboard/30/dashboard

Steps to reproduce the bug

1. Go to puzzle dashboard
2. Select a number of days larger or equal to 21 days in which you have played no puzzles

What did you expect to happen?

No error in the console

What happened instead?

Console error "Failed to create chart: can't acquire context from the given item" is displayed.

Operating system

Windows 11

Browser and version (or alternate access method)

Brave desktop

Additional information

It's weird that the same problem doesn't happen for intervals of less than 21 days.

The error seems to be a chart.js one, originating from here:

The code does check if there are datasets to be loaded, but there is always the "Performance" dataset, so it goes through.