presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/file/FileHiveMetastore.java/RoleGranteeTuple/RoleGranteeTuple
class RoleGranteeTuple:        private RoleGranteeTuple(String role, HivePrincipal grantee)
        {
            this.role = requireNonNull(role, "role is null");
            this.grantee = requireNonNull(grantee, "grantee is null");
        }