Add a check if
is not null.
This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.
Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"
The code has different problems. The exception handling is too local. This is how you can catch all non-specific exception on top of UI thread, in the main event-oriented cycle:
Catching an Exception
. Avoid hard-coding of immediate constants
, explicitly define constants.