The JMX spec document says:
"jmx.monitor.error.type - Sent when the object instance of the observed attribute value is null or not of the appropriate type for the given monitor...."
But the current implementation simply ignores null-valued attributes. Either the spec or the implementation should be fixed.

In favour of fixing the spec, we may consider that a null value indicates that the attribute is currently unavailable. Returning null causes the monitor to be effectively suspended while that is true.

###@###.### 2004-11-24 17:44:25 GMT

The monitor implementation has been fixed to follow the spec.
A MonitorNotification of type jmx.monitor.error.type is sent
when the object instance of the observed attribute value is
null.

###@###.### 2005-1-26 13:47:20 GMT