[Bug Report][2.6.0] v-data-table sortBy / sortDesc attributes are not reset correctly

[boris-graeff]

Environment

Vuetify Version: 2.6.0
Vue Version: 2.6.14
Browsers: Chrome 95.0.4638.69
OS: Linux x86_64

Steps to reproduce

Click four times on the header of the same column (eg: calories) and look at the logs :

1/ {sortBy: 'calories', sortDesc: false} => ok
2/ {sortBy: 'calories', sortDesc: true} => ok
3/
{sortBy: undefined, sortDesc: true}
{sortBy: undefined, sortDesc: undefined}
4/
{sortBy: Array(1), sortDesc: undefined}
{sortBy: Array(1), sortDesc: Array(1)}

Expected Behavior

We are expecting string/boolean couple ({sortBy: 'calories', sortDesc: false}) as multi-sort property is false

Actual Behavior

We got a array/array couple ({sortBy: Array(1), sortDesc: Array(1)})

Reproduction Link

https://codepen.io/boris-graeff/pen/NWvmmZJ?editors=101

Other comments

Not sure about what we should have in step 3 (undefined/undefined or empty string / false ?)

[jelle-eastground]

Since this update, I discovered that options of v-data-table initially contains the following by default:

sortBy: [],
sortDesc: [false],  // previously []

Isn't that inconsistent, as the (number of) items of sortDesc should always match the (number of) items of sortBy? At least this change introduced some bugs in my application I had to tackle.