Conditional Formatting: determine when a cell if blank

At work, I needed that if the value of a cell is equal to the cell next to it, then the bg color changes to red, but it is doing it for blank cells, so it may be confusing for others. Is there a way to avoid blank cells? I have this formula: =IF($D2=$C2,TRUE) then bg color changes to red (not sure if the correct formula, but it worked at the beginning, I am doing this in the Conditional Format Rules in Google Spreadshets)

Thanks in advance!