[Bug Report] v-data-table group doesn't work when value has "node.*" in it, i.e. reply from graphql-apollo.

[ivanvorona]

Environment

Vuetify Version: 2.2.6
Vue Version: 2.6.10
Browsers: Chrome 78.0.3904.108
OS: Windows 10

Steps to reproduce

create a v-data-table with grouping
Group by node.vendorSeqno
See, that the table says that value is undefined.

Expected Behavior

Grouping to work

Actual Behavior

grouping doesn't work.

Reproduction Link

https://codepen.io/ivorona/pen/VwYRpMY?editors=1010