VBA - Autofill To First Blank Adjacent Column?

I want to write some VBA code that simulates the double click of the square in the lower right of a selected cell. When you double click it, it fills every cell in column A until the first blank in column B. I was able to find this code searching around:

Code:
Selection.AutoFill Destination:=Range("A10:A" & Range("B10" & Rows.Count).End(xlUp).Row)
Selection.Copy

The issue with the above is that it copies the data all the way down to the LAST row in column B with data.

I want to have the macro stop when it finds the FIRST blank cell in column B.

Just as an example, the last row of data in column B is 100, but in row 67 the cell is blank, so I want it to stop at row 66.