formula to make data plot on graph correctly

morning all , i have attached a few relevant columns of a sheet i need help with please.

column B is a monetary daily P&L value
column F is basically an accumulative values of column B

The problem i have is i run a graph (sheet COMB) from the data in column F so i need it to not plot the future
days when not populated hence i have them as #N/A while not populated

what im trying to do is
keep column F accumulating the data that is returned in column B but whilst keeping the future cells at #N/A to make it plot correctly on my graph

the formula that is in column F now is what i have been trying myself and it does not work

thanks in advance
will