Update a task with the following due_at dates:
It appears you use the unix epoch start date to clear the due_at property, but this is unexpected given I can use a date from before the epoch start date and it’s correctly set (first bullet). In order to clear the value sending a request with “due_at:null” is sufficient.
Are you coming from the future and trying to set yourself up some tasks for then you travel back to the past? 
Yup. That is exactly what I’m trying to do 
The problem is I receive unexpected result for one particular date. Any other date later than 100AD (sic!) works fine, based on our tests.
What makes “1970-01-01T00:00:00+0000” special? Is it a bug? Should I avoid setting due dates in the past? Maybe a 400 Bad Request would be better in this case, for date values that are not allowed.
It is Epoch time, kinda special date indeed Unix time - Wikipedia
Yes, I’m aware of that, but I still think it’s a bug, see my first comment. Using it to clear the due date is unexpected.
I could see a code where the date stored is the number of secondes from epoch and when it stores zero that clears the field ^^ nice bug =) not sure they will prioritize a fix though 
Yup, I’m pretty sure this is the case. Fair enough with not fixing it any time soon, it’s a minor issue. Just wanted to confirm it’s a bug on the Asana side. Thanks!