BUG #17762: date field casts to null in case section with join's

The following bug has been logged on the website:

Bug reference:      17762
Logged by:          Evgeny Nee
Email address:      jounts@gmail.com
PostgreSQL version: 15.1
Operating system:   debian 11
Description:

Query works fine:
SELECT id, 
CASE
    WHEN date_field IS NOT NULL THEN date_field::TEXT
END AS date_str
FROM my_table

But this query:
SELECT t1id, t2.name, 
CASE
    WHEN t1.date_field IS NOT NULL THEN t1.date_field::TEXT
END AS date_str
FROM my_table t1
JOIN my_table2 t2 ON t1.id = t2.id

returns: null in date_str