Unusual behaviour in template queries

Please move this if it needs to be elsewhere.

I’m using 6.0.0. I accidentally selected “value groups” to enabled but did not add a query or tags. I kept getting “unexpected end of json” which I assumed was down to a fault in my variable query - from Chrome debugger:

filters.ts:4 store updating angular $location.url /d/L5Hn0w-mkwe/ep-winlogbeat-mq-events?orgId=1 DashboardGrid.tsx:171 SyntaxError: Unexpected end of JSON input at JSON.parse (<anonymous>) at Object.ge [as fromJson] (angular.js:1471) at e.metricFindQuery (datasource.ts:464) at e.metricFindQuery (datasource_variable.ts:94) at e.updateTags (datasource_variable.ts:44) at angular.js:17051 at angular.js:17095 at l.$digest (angular.js:18232) at l.$apply (angular.js:18531) at angular.js:18832

When I disabled “value groups/tags” the problem went away. Is there a good reason that a user can select “value groups/tags” without populating at least one of the two input fields ?