oldest I can go at the moment is Excel 2000, I created a test spreadsheet
1. Put formula in both H9 and I9
2. placed values in H7 and H8 (19 and 12 respectively)
3. Applied conditional formatting to H9.
(I've also left D12 blank).
H9 and I9 both display the same value, with H9 having colour formatting. With a value in F7 they both show "31" with H9 being coloured orange. If I delete the contents of F7, they both display 0 and H9 is coloured Yellow. I couldn't notice any difference between when conditional formatting was on the cell and when it wasn't.
You've described the formula intent as showing blank if there is no value in F7, however, The way the IF is structured, then if F7 has no entry, then H9 will have the value in D12.
Further, even if D12 is blank itself, the value will be converted to a number because the other IF Expression has a Numeric result. If you want it to be blank you can instead indicate that directly in the expression, instead of the value in D12:
=IF(F7<>"",(SUM(H7:H8)+D12),"")