Assembly: System.Web (in system.web.dll)
A string that represents an event argument to pass to the event handler.
When a null reference (Nothing in Visual Basic) is used as the event argument parameter, the string is serialized to "null" and sent back to the server. Because there is no way to distinguish between a null reference (Nothing in Visual Basic) and "null", you should avoid using a null reference (Nothing in Visual Basic) argument parameters with callbacks.
Exceptions thrown in RaiseCallbackEvent will not prevent GetCallbackResult from being called and returning a result. To prevent GetCallbackResult from returning a result, set a flag when an exception is thrown in RaiseCallbackEvent and return an empty string from GetCallbackResult.