How can I make a formula ignore a blank cell in Google sheets

I am creating a budget template and have a formula that multiplies cells. However, not every cell will have a number in it. How do I make it so the formula will ignore blank cells or make them = 1 instead of = 0?

(Example: formula is =B1*B2*B3. In some rows, B3 is empty, in other it has a value. In other rows, B2 is empty, but B1 and B3 have values. How do I create a formula that ignores or counts empty cells as 1 to make the formula work across the board?)