Empty string equality expression transpiles to an always-false query in Django + Oracle

[JPDSousa]

Describe the bug
Expressions involving an equality operator and an empty string always evaluate to false when using Django + Oracle. This seems to be specific to the Django transpiler.

To Reproduce
Here's a test case that reproduces this behavior:

import pytest
from django.contrib.auth.models import User
from scim2_filter_parser.transpilers.django_q_object import get_query


@pytest.mark.django_db
def test_filter_empty_string_fails() -> None:
    user = User(username='dummy_username', first_name='')
    user.save()
    query = get_query(
        'name.givenName eq ""', {('name', 'givenName', None): 'first_name'}
    )

    assert list(User.objects.filter(query)) == [user]

Which fails with:
tl;dr: The query returns no results

>       assert list(User.objects.filter(query)) == [user]
E       assert [] == [<User: dummy_username>]
E         
E         Right contains one more item: <User: dummy_username>
E         
E         Full diff:
E         + []
E         - [
E         -     <User: dummy_username>,
E         - ]

The generated query is:

SELECT 
    "AUTH_USER"."ID", "AUTH_USER"."PASSWORD", "AUTH_USER"."LAST_LOGIN", "AUTH_USER"."IS_SUPERUSER", "AUTH_USER"."USERNAME", "AUTH_USER"."FIRST_NAME", "AUTH_USER"."LAST_NAME", "AUTH_USER"."EMAIL", "AUTH_USER"."IS_STAFF", "AUTH_USER"."IS_ACTIVE", "AUTH_USER"."DATE_JOINED" 
FROM "AUTH_USER" 
WHERE UPPER("AUTH_USER"."FIRST_NAME") = UPPER('')

Expected behavior
The generated query should find dummy_username.

Environment:
Python version: 3.11.7
Django version: 4.2.12
scim-filter-parser version: 0.5.1

Additional context
According to this article (and my own tests via sqlplus), UPPER("AUTH_USER"."FIRST_NAME") = UPPER('') will always evaluate to false, even when "AUTH_USER"."FIRST_NAME" is an empty string.

[logston]

Thank you for this bug report! Unfortunately, we have a very low capacity work on this at the moment. I am happy to review PRs if you would like to make this change to support Oracle.

[JPDSousa]

No worries! I got a proposal for a PR we can start with. I'll open it as soon as I have some free time.