Fill down to last cell containing data

Hi
I am sure this is probably a quick fix but I can't get my head around the solution.

I have the following code:

    Sheets("Export").Select
    Range("A3").Select
    ActiveCell.FormulaR1C1 = "=Import!R[7]C" ' = Date
    Range("B3").Select
    ActiveCell.FormulaR1C1 = "=Import!R[7]C&"" - ""&Import!R[4]C[1]" ' = Concatenate type & description
    Range("C3").Select
    ActiveCell.FormulaR1C1 = "=Import!R[7]C[1]" ' Debit
    Range("D3").Select
    ActiveCell.FormulaR1C1 = "=Import!R[4]C[1]" ' Credit
' Fill down to next row
    Range("A3:D3").Select
    Selection.AutoFill Destination:=Range("A3:C4"), Type:=xlFillDefault
    Range("A3:D4").Select

What I need to do is to continue to fill down until " " (or a null value) is found within A*:D*


Please can anyone help me ?