proposal: ignore null fields in not relation type composite type based constructors

Hello

In Czech Postgres mailing list was user request for serialization to json
without null values.

He needs a similar behave like XMLFOREST has - it ignores NULLs

In some situations and conversions, when your table is +/- sparse matrix,
this request is valid

postgres=# select hstore(omega) from omega;
hstore
─────────────────────────────────
"a"=>"10", "b"=>"20", "c"=>NULL
"a"=>NULL, "b"=>"20", "c"=>"30"
(2 rows)

Proposed function

postgres=# select hstore(omega, ignore_nulls := true) from omega;
hstore
─────────────────────────────────
"a"=>"10", "b"=>"20"
"b"=>"20", "c"=>"30"
(2 rows)

What do you thinking about this proposal?

Regards

Pavel