Fixes #20585: Fix AttributeError exception for conditionless single-field UniqueConstraints

[jeremystretch]

Fixes: #20585

Tweak logic in the monkey patch to handle UniqueConstraints without a condition.

[jeremystretch]

@pheus if you're available, could you check whether this resolves the issue for you?

[pheus]

I can confirm that this fixes the issue for my case. Thanks for the fast fix!

[jnovinger]

Verified with:

./manage.py shell -c "
from django.db import models
from netbox.monkey import get_unique_validators

class TestModel(models.Model):
    name = models.CharField(max_length=100)
    class Meta:
        app_label = 'test'
        constraints = [
            models.UniqueConstraint(fields=['name'], name='test_name_unique')
        ]

field = TestModel._meta.get_field('name')
try:
    validators = list(get_unique_validators('name', field))
    print(f'Fix verified - returned {len(validators)} validators')
    for v in validators:
        print(f'   Validator: {v.__class__.__name__}')
except AttributeError as e:
    print(f'Bug present: {e}')
    import traceback
    traceback.print_exc()
"