E.g. if you have a "tax ID" column, and two people in your database don't have tax IDs because they're not <your country> tax payers. Or "payment vendor proces

E.g. if you have a "tax ID" column, and two people in your database don't have tax IDs because they're not <your country> tax payers. Or "payment vendor processing ID". You may have multiple entries not yet sent to the vendor, so they're NULL. This shows up literally all the time in SQL schemas.