Duplicate data from field above if cell is blank

Ok so my data is set up like this

Client Account Number Payment
ABCD 12345678 £20.00
10203040 £40.00
Total £60.00
EFGH 12131415 £10.00
16171819 £20.00
17852654 £20.00
Total £50.00

Imagine that Client is Cell reference "A1". I need a code that will look at column A and if the cell is empty it will duplicate the writing from above so Cell "A2" will be duplicated into Cell "A3". I also need it to stop when it reaches the bottom of column A. The bottom will be signified by Cell value "**".

The code I have so far is:

Sub Duplicate_Client()

Range("A2").Select
If Not IsNull(ActiveCell.Value) Then ActiveCell = ActiveCell.Offset(-1, 0)
ActiveCell.Offset(1, 0).Select
Loop

Application.ScreenUpdating = True

End Sub

Thanks