Re: Bug with plpgsql handling of NULL argument of compound type

There is a rather squishy question as to whether NULL::composite_type
should be semantically equivalent to ROW(NULL,NULL,...)::composite_type.
If it is, then the SELECT should have failed before even getting into the
plpgsql function, because ROW(NULL,NULL) is surely not a valid value of
type c.  The SQL standard seems to believe that these things *are*
equivalent (at least, that was how we read the spec for IS [NOT] NULL).

FWIW, there is a very good argument that any not-null restriction on a
datatype (as opposed to a stored column) is broken by design.  How do
you expect a LEFT JOIN to a table with such a column to work? 

We
certainly are not going to enforce the not-nullness in that context,
and that leads to the thought that maybe we should just deny the validity
of such restrictions across the board.