Java's org.postgresql.util.PSQLState is missing common PostgreSQL Error Codes

In my Java API server, I am using SERIALIZABLE transaction isolation mode, so I'm specially handling the error code of "40001 serialization_failure", which can occur often. I'm getting the error code String using SQLException's getSQLState() function.

Therefore I was surprised to see that the Java enum org.postgresql.util.PSQLState does not include this error code.

PSQLState code: https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/java/org/postgresql/util/PSQLState.java
PSQLState documentation: https://jdbc.postgresql.org/development/privateapi/org/postgresql/util/PSQLState.html

The 40001 serialization_failure error is listed here: https://www.postgresql.org/docs/11/errcodes-appendix.html

It seems like this should be added to the pgjdbc Java enum. Is there a reason it's not in there?