Getting this error is DevTest IAM server.log when logging in with LDAP credentials to IAM:
2019-03-14 15:17:00,676 ERROR [org.keycloak.services.error.KeycloakErrorHandler] (default task-38) Uncaught server error: org.keycloak.models.ModelException: User returned from LDAP has null uuid! Check configuration of your LDAP settings. UUID Attribute must be unique among your LDAP records and available on all the LDAP user records. If your LDAP server really doesn't support the notion of UUID, you can use any other attribute, which is supposed to be unique among LDAP users in tree. For example 'uid' or 'entryDN' . Mapped UUID LDAP attribute: objectGUID, user DN: cn=USER2,ou=internal,o=key
LDAP server being used does not support the notion of UUID.
Within IAM, set the value of "UUID LDAP Attribute" to uid on the User Federation Settings page.