Processes a callback event that targets a control.
Assembly: System.Web (in System.Web.dll)
When null 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 null and "null", you should avoid using null argument parameters with callbacks.
Exceptions thrown in 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 and return an empty string from GetCallbackResult.