anchor.diff:          print(e);
           // Errors thrown by MongoDatabase are Map objects with fields err, code,
           // ...
  -        throw new MongoException(e);
  +        _release_locks().then((_) {
  +          throw new MongoException(e);
  +        });
         }
         ).then((_) => _release_locks());
     }
  
positive.code:         print(e);
          // Errors thrown by MongoDatabase are Map objects with fields err, code,
          // ...
          throw new MongoException(e);
        }
        ).then((_) => _release_locks());
    }
  
negative.code:         print(e);
          // Errors thrown by MongoDatabase are Map objects with fields err, code,
          // ...
          _release_locks().then((_) {
            throw new MongoException(e);
          });
        }
        ).then((_) => _release_locks());
    }
  