Need filter function to return blank if blank and 0 if 0

I have a formula to retrieve the value in a **unique** cell via filter. `=filter(range, condition*condition*condition)`. However, sometimes I am filtering to older data from before this particular point was collected and the records are blanks. This is currently showing as 0 when retrieved and the preferred behavior is showing NA(). Changing all retrieved 0s will not work, as some of the real data has actual zeroes. It needs to remain numbers, so adding &"" after the range will not work. I have also tried `=if(isblank(filter()),na(),filter())`, and it still returned 0. Manually changing the source data is not an option, as the input data is about 25k rows that change daily, copied in from a SQL query.