Searching for users against the REST using CQL returns empty accountType fields

Issue Summary

Querying the REST API with /wiki/rest/api/search/user?limit=20&cql=type=user returns results where user.accountType is always a blank string.

Steps to Reproduce

1. Log in to confluence.
2. Open [base-url]/wiki/rest/api/search/user?limit=20&cql=type=user in a new tab

Expected Results

The user.accountType field of each result is populated.

Actual Results

The user.accountType field of each result is NOT populated.

Workaround

To work out the account type, query /wiki/rest/api/user?accountId=[account-id].