Function pg_get_constraintdef

SELECT pg_get_constraintdef(c.oid)
FROM pg_catalog.pg_constraint c;

If I execute the query in two different servers with PostgreSQL 17.1 and in different databases in these servers, then I get the answer

ERROR:  invalid constraint type "n"

In case of an empty database I do not get the error. The query worked in the servers before upgrading to PostgreSQL 17.

If I execute the query in a database of a server with PostgreSQL 15, then I do not get the error. 

Best regards

Erki Eessaar