Sys.ArgumentNullException
Raised by the Microsoft Ajax Library framework when an argument has an invalid value of null.
Remarks
When a client function or method is called with an argument that has an invalid value of null, a Sys.ArgumentNullException object is created by using the Error.argumentNull function.
For more information about how to raise this error, see Error.argumentNull Function.
For more information about how to handle error conditions, see Debugging and Tracing Ajax Applications Overview.