make a Year to date column

Can someone please suggest how I can get the year to day column display
Nothing if there is not anything in the preceding column?

Eg... Column K is YTD. Column J is Invoice total. I figured out how to
hide the zeros in the J column... but can't figure out how to make K show
nothing until there is a figure in J.

Its a simple sheet. Just adds invoices.. and provides a YTD figure. But
looks DUMB when the last YTD figure is carried all the way down the column.

Thank you ...