Earliest date that has empty cell next to it, from list of dates

Hi
I have a table of tasks with due dates in a column and a column which indicates if tasks are complete. I have a cell above the table which should display the earliest due date of incomplete tasks - that is the cell (d1) I would like a formula for. I would like to meet the requirement without having a formula that must be copied down in an additional column in the table.

Notes:
If a task is complete it will have "y" in the "Complete?" column and if it is incomplete there will be nothing in the "Complete?" column.
The list of tasks may be long or short and will change regularly.
The tasks are not necessarily sorted according to due date.
Not all of the tasks have due dates.

I have an example below showing the desired result. Thanks for any assistance.
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