Excel IF Function, True, False, or Blank

Currently trying to compare two dates to work out whether a document has been submitted within SLA dates

I have 3 cells,

H5 (SLA target date)
T5 (Document submitted date)
U5 (In SLA or Not) Y/N

Using really simple formula in

U5 of =IF(T5-H5 <= 1, "Y", "N")

But the formula is returning true down the column for cells which contain no content yet.

How do I return either a Y, N, or 0 (or blank) in column U?