Split Y Line chart on hover label issue

[JHawk]

Bug Report

Steps to Reproduce:

1. Go to https://perspective.finos.org/blocks/editable/index.html
2. Set plugin to "Y Line"
3. Select columns "Quantity" and "Sales" by Shift Clicking the columns in the config panel
4. Split "Quantity" to the right axis by clicking the "Quantity" label on the chart
5. Deselect the "Sales" column by clicking "Sales" in the legend
6. Hover over the chart

Expected Result:

A rendered label when hovering the chart

Actual Result:

No rendered label and a stream of console errors (screenshot)

Environment:

v2.7.2, tested on macOS and Linux in Chrome