Re: Extended Statistics set/restore/clear functions.

>
> It seems to me that this comes down to the text[] representation when
> we read this data from the catalogs, where we can just rely on NULL
> being in the value, and the official marker in this case:
> https://www.postgresql.org/docs/current/arrays.html#ARRAYS-INPUT

And we're doing a lot of casting ANYARRAY to text throughout this and the
attribute stats, so that our assurance that we can live without nulls.

Perhaps we have a couple of specific cases where checking for we want
> some NULL-ness knowledge? It would be less expensive than a full
> array deconstruction, for sure, especially if the MCVs are large text
> values.
>

It's a good theory, or maybe the original coder just assumed that the
caller of pg_mcv_list() SRF could lateral-unnest the output and keep only
the interesting columns.

Rebasing and null-rip-out underway.