Dear fellow hackers,
This polymorphic function produces an error if the input value is null,
otherwise it returns the input value unchanged.
This need for this function originates from the discussion
"Assert single row returning SQL-standard functions" [1].
/Joel
[1] https://www.postgresql.org/message-id/flat/9233b657-696f-430f-9557-dc602a2b9e0e%40app.fastmail.com