Ranger usersync fails to sync users when a duplicate user exists in ranger

Ranger is having issue with syncing user with case sensitive when the backend database for ranger is MySQL / Maria DB. Initially users are sync'd with default configuration (without any case conversion). Later usersync is configured to sync users with upper case. At this time, usersync fails to sync any users throwing duplicate user exception. For resolving this, existing user from ranger must be deleted and then restarted the usersync service. Instead, ranger code should update existing user with case conversion and continue.