BUG #16868: Cannot find sqlstat error codes.

The following bug has been logged on the website:

Bug reference:      16868
Logged by:          bipsy Nair
Email address:      nbipin29@gmail.com
PostgreSQL version: 12.4
Operating system:   RDS and EC2
Description:

Hi,

I am not able to get any SQLSTATE Error code for Postgres on any versions on
RDS AWS or EC2 Postgres 10.

ERROR: No SQLSTATE genrated in Postgres. This was the error's which was
displayed.
=====
ERROR:  duplicate key value violates unique constraint
"pk_dml_error_logging"
DETAIL:  Key (id)=(1) already exists.

I am looking for a Error code like '23503' as per PG documentations
https://www.postgresql.org/docs/current/errcodes-appendix.html#ERRCODES-TABLE

Our developer needs a Error code generated so that they can trap in the
applications incase of any errors.
Please advice and provide a workaround.