relpages value for partitioned tables

I noticed in src/backend/commands/analyze.c, do_analyze_rel(), the value
for relpages for partitioned tables is stored as -1:

/*
* Partitioned tables don't have storage, so we don't set any fields
* in their pg_class entries except for reltuples and relhasindex.
*/
vac_update_relstats(onerel, -1, totalrows,
0, 0, hasindex, InvalidTransactionId,
InvalidMultiXactId,
NULL, NULL,
in_outer_xact);

I don't see any documentation or explanation of this, and it doesn't
seem to be made use of anywhere.

Other relation kinds without storage (views, partitioned indexes) store
0 in relpages.

If we wanted to keep this special value somehow, then it might at least
make more sense to write InvalidBlockNumber, because the relevant
argument type of vac_update_relstats() is actually BlockNumber (not
int32 as in the catalog).

But we should probably be consistent across relkinds?

Thoughts?