I am needing to create a formula to add 7 days to a certain date entered, but if no date is entered I need the cell to remain blank

EX.
A1 blank C1 blank
A1- 2/1/2015 need C1 2/8/2015
and so on for the remaining cells that will follow down the sheet

Any help would be appricated as I am not an excel guru

Thanks