How can I copy values from one cell in a column down to the next cell IF the
2nd cell is blank, For example:

A1 = 20
B1 =

I want the value of A1 to be copied to B1 if B1 is blank/contains a value of
Null, I have about 11,000 records like this, whe If the next cell in the
column is blank, then I need to copy the previous cells data into that cell.