Steps:
1. Login to JIRA.
2. Write a query like assignee in memeber of ("JIRA-users").
3 Click on search to run the query.

Result:
1. It give error message "Function 'membersOf' can not generate a list of usernames for group 'JIRA-users'; the group does not exist.
2. The group name parameter in member of function is case sensitive.

Expected:
1. Like all places in JQL, group name should be not case sensitive.