Date/time Custom Attributes cant be save empty?
Something I miss?
You can change how this value displays by copying the file concrete/models/attribute/types/date_time/controller.php to models/attribute/types/date_time/controller.php and changing the getDisplayValue() method to whatever value you want to display in that special case.
I would think that if there was no date, then the whole datetime field should be NULLed out. Have there been any conversations on this that you know of?
There is not much info about this in the forum.
Otherwise you need to do what tbcrowe suggests and alter the code that gives you the values so it converts 0 to null in php.
I looked over the code I referenced above some more, though, and you may also need to change the form() method in that file.
I mean in the core.
It's just confusing when a user delete the data of a custom date attribute and when he edit it back, it as save 1969-12-3 instead of NULL.
You should file a bug for this and provide as much detail as possible -- there are just so many parts of the system it's impossible for Andy and team to know about everything unless people bring it to their attention.
Better yet, if you're a programmer you could code up a solution and test it out, and if it works you can make a patch and submit that (thus greatly increasing the likelihood that the change will get implemented).