FEATURE REQUEST: Set a task due date without a start date

Please provide the ability to set a task due date without a start date. Not all tasks need duration details, but may just have deadlines.

And vice versa, a start date without a due date. To explain why this is needed, I sometimes create a task and assign it to someone else who will then be able to properly define the end date (as they are the ones allocating time for it). So I define the start, but they define the end date later on. Right now if you dont enter both , the input is rejected.