Mouseover and Legend selections don't work together

[mershal]

Quick overview of the issue

I want one chart that does 2 things:

1. Hovering a bar should change its opacity
2. Clicking on a legend item reduces the opacity of all the unselected items

For this, I created 2 selection params and used them in fillOpacity condition.
The error starts when I first click a legend item, and then when I hover the legend.

The error is:
TypeError: Cannot read properties of undefined (reading '0')

After this error the entire chart go nuts:

1. I need to double click a legend item to select it (instead of a single click)
2. Clicking on a bar (might) change the selected legend item
3. Hovering a bar doesn't always change its opacity
4. And maybe some other stuff

Simple spec to reproduce the issue

Example in Vega Editor

{
  "$schema": "https://vega.github.io/schema/vega-lite/v5.json",
  "data": {
    "values": [
      {"category": "A", "value": 1},
      {"category": "B", "value": 2},
      {"category": "C", "value": 3}
    ]
  },
  "params": [
    {"name": "hover", "select": {"type": "point", "on": "mouseover"}},
    {
      "name": "legend",
      "select": {"type": "point", "fields": ["category"]},
      "bind": "legend"
    }
  ],
  "mark": {"type": "bar"},
  "encoding": {
    "x": {"field": "category", "type": "ordinal"},
    "y": {"field": "value", "type": "quantitative"},
    "fillOpacity": {
      "condition": [
        {"param": "legend", "value": 1},
        {"param": "hover", "value": 0.6, "empty": false}
      ],
      "value": 0.2
    },
    "color": {"field": "category"}
  }
}

Screenshot of the error

Any quick solutions?
Thanks!

[arvind]

Thanks for filing this issue @mershal! This should be fixed as of #8268.