A blank/empty cell is not the same as zero/0.
May the code below guide you. First clear the cell (A1) and run the code, then put a zero in the cell and run the code again and you will see.
If Range("A1") = vbNullString Then Range("A1").Value = "Cell was blank"
If Range("A1") = 0 Then Range(" A1").Value = "Cell contained a zero"