ValueError: None is not a valid TransactionPriority with version 26.0.0

Hi,

I'm using Robot Framework DatabaseLibrary with oracledb driver, oracledb was updated to 26.0.0 and it started getting this error.
Note that below analysis was done with Copilot.

Problem
When establishing a connection in thin mode (default) against a database version that does not support the new Transaction Priority feature (or when the server handshake returns None for transaction priority), oracledb.connect() fails with:

ValueError: None is not a valid TransactionPriority

Details

1. What versions are you using?
   26.0.0

Give your Oracle Database version, e.g.:
19.28 (should be applicable to 19c or older / pre-23.26.2)

Give your Oracle Client version (if you are using Thick mode):
I'm using thin mode

Python 3.11 Linux 64

2. Is it an error or a hang or a crash?
   Error

3. What error(s) or behavior you are seeing?

Traceback (most recent call last):
  File ".../test.py", line 4, in <module>
    conn = oracledb.connect(
  File ".../oracledb/connection.py", line ..., in connect
    ...
ValueError: None is not a valid TransactionPriority

4. Does your application call init_oracle_client()?
   I'm using thin mode

This tells us whether you are using the python-oracledb Thin or Thick mode.
Thin mode

5. Include a runnable Python script that shows the problem.

import oracledb

conn = oracledb.connect(
    user="my_user",
    password="my_password",
    host="my_db_host",
    port=1521,
    service_name="my_service_name",  # or sid="my_sid"
)

print("Connected:", conn.version)
conn.close()

Start with the oracledb.connect entry point and the connection.py location shown in the traceback. Reproduce the failure with the provided Python script in thin mode against the stated database versions, then verify that a server returning None for transaction priority can connect without raising ValueError.