Issue with History. registerCallback() if history id is null

[ramya123]

Is there any way i can prevent calling callback method which is registored with History.registerCallback(). If History id is null
Documnetaion says like this
When the user transitions to the history entry immediately before the first synthetic history entry, the callback is fired with an id of null. Is there any way to stop calling registered callback if the id is null

http://www.smartclient.com/smartclie...gisterCallback

[Isomorphic]

What would be the purpose of this? If you don't want to take action in this circumstance, just exit your callback function.