What's the Postgres error?

    master441=# begin;
    BEGIN
    master441=# insert into metric (metric_name, metric_value, metric_module)
    master441-# values ('removeme', 't', 'no_module')
    master441-# returning metric_id;
     metric_id 
    -----------
           324
    (1 row)
    
    INSERT 0 1
    master441=# rollback;