Why is NULL a bad thing? Sometimes I absolutely want to know if a field is NULL, so i can coalesce to the desired value. I know this is SQL Server specific, sin

Why is NULL a bad thing? Sometimes I absolutely want to know if a field is NULL, so i can coalesce to the desired value. I know this is SQL Server specific, since Oracle treats empty strings and NULLs the same, but that approach has always felt wrong to me. Thoughts? Edit: I see maybe that I should have scrolled down further before posting this. Lots of discussion further down about NULL values.