If you want to set a date field to an empty date or need to compare if a date field is empty, you can use the datenull() function. It is a method of the Global class and will simply return 01\01\1900.This leads to more things:
You can write dates in Axapta X++ editor using backslashes, e.g. 14\04\2006
An empty date in Axapta is specified as January 1st, 1900.
You can use methods from the Global class without having to write "Global::". So, you can write "if date == datenull()" and you do not have to write "if date == Global::datenull()". This works with all the methods from the Global class.