Replace multiple words in a row

Ah, I think the issue must be earlier then.

Try putting the null check in earlier:

Text.Combine(
    List.Transform(
        Text.Split(if [Original] = null then "" else [Original], ","),
            each
                if      _ = "100000011" then "Declared bankruptcy"
                else if _ = "100000014" then "Filantropic school"
                else if _ = ""          then "non-qualified"
                 else "Verify"
        ),
        ","
    )
)