Equation that doesn't calculate unless ALL relevant values are present

I'm creating a ledger with a "Coins Remaining" value in column J that is dependent upon the most recent value of "Coins In/Out (+/-)" in column I. Simply stated each value in J is equal to the sum of the cells directly to the left and directly above (J9=I9+J8).

This function is simple but I'd like to perpetuate the entire "Coins Remaining" column with this formula in such a way as to only calculate when there actually IS a value in I, and NOT when it is empty. Essentially, if there is no corresponding value in the "Coins In/Out (+/-)" column, I would like the same to be true of the "Coins Remaining" column as well.

Is this possible?