UQL does not accept capitalized boolean operators

Issue Summary

User Query Language is documented as accepting capitalized boolean operators, but such queries fail with the error "Unable to parse UQL".

The example query in the reference documentation at https://developer.atlassian.com/cloud/jira/platform/rest/v3/api-group-user-search/#api-rest-api-3-user-search-query-get is as follows: 

is assignee of PROJ AND [propertyKey].entity.property.path is "property value"

This issue has been raised in response to https://community.developer.atlassian.com/t/search-users-by-query-docs-are-wrong/51569.

Steps to Reproduce

1. In a browser, log into a Jira tenant such as https://ecosystem.atlassian.net.
2. Invoke the Jira API with a UQL search including an uppercase boolean operator such as https://ecosystem.atlassian.net/rest/api/3/user/search/query?query=is%20assignee%20of%20ACJIRA%20OR%20is%20assignee%20of%20ACJIRA

Expected Results

User search results are returned.

Actual Results

The following error response is returned:

Unable to parse UQL

Workaround

Change the boolean operator to lower case. e.g. https://ecosystem.atlassian.net/rest/api/3/user/search/query?query=is%20assignee%20of%20ACJIRA%20or%20is%20assignee%20of%20ACJIRA