Missing Group Key in grouped aggregate

Hello,

I noticed that, beginning with PG16, grouped aggregates are missing the "Group Key" in the EXPLAIN output.

It seems the Agg node has numCols (number of grouping cols) set to zero in queries like

SELECT foo, count(*) FROM bar WHERE foo=1 GROUP BY foo;

In PG15, the "Group Key" is shown and the Agg node has numCols set as expected.

Is this intentional or a bug?

Best regards,

Erik