Nested queries broken

Using the current version 0.8.0 of the Mirage Chrome Extension, whenever the checkbox "Add joining quere" is selected and "nested" is selected from the "select-joining-query" dropdown, the generated query changes to `{}` instead of generating the nested query wrapper.

Tested on Chrome Canary 70.0.3524.0.

Reproduce the issue in the Mirage Chrome Extension by selecting “Add joining quere” and choosing “nested” from the “select-joining-query” dropdown. Inspect the query-generation path for this selection and compare its output with the expected nested query wrapper. Done means the generated query is no longer `{}` and correctly contains the nested wrapper.

Written by the indexing model from the issue text.