presto-hive/src/main/java/io/prestosql/plugin/hive/metastore/file/FileHiveMetastore.java/FileHiveMetastore/listRoleGrantsSanitized
class FileHiveMetastore:    private synchronized Set<RoleGrant> listRoleGrantsSanitized()
    {
        Set<RoleGrant> grants = readRoleGrantsFile();
        Set<String> existingRoles = listRoles();
        return removeDuplicatedEntries(removeNonExistingRoles(grants, existingRoles));
    }