Make stxstattarget nullable
To match attstattarget change (commit
4f622503d6d). The logic inside
CreateStatistics() is clarified a bit compared to that previous patch,
and so here we also update ATExecSetStatistics() to match.
Reviewed-by: Tomas Vondra <tomas.vondra@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/
4da8d211-d54d-44b9-9847-
f2a9f1184c76@eisentraut.org