From 634681a72e9cdb1fefcf5779eceb8ec95ae6c13f Mon Sep 17 00:00:00 2001
From: Jeremy Stretch <jstretch@netboxlabs.com>
Date: Tue, 26 Dec 2023 13:15:23 -0500
Subject: [PATCH] Fixes #13606: Fix filtering by null for multiselect custom
 fields

---
 netbox/extras/models/customfields.py     |  4 +---
 netbox/extras/tests/test_customfields.py | 13 +++++++------
 netbox/utilities/filters.py              | 16 ++++++++++++++++
 3 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/netbox/extras/models/customfields.py b/netbox/extras/models/customfields.py
index f70812bc075..ff887ddeb97 100644
--- a/netbox/extras/models/customfields.py
+++ b/netbox/extras/models/customfields.py
@@ -10,7 +10,6 @@
 from django.core.validators import RegexValidator, ValidationError
 from django.db import models
 from django.urls import reverse
-from django.utils.html import escape
 from django.utils.safestring import mark_safe
 from django.utils.translation import gettext_lazy as _
 
@@ -571,8 +570,7 @@ def to_filter(self, lookup_expr=None):
 
         # Multiselect
         elif self.type == CustomFieldTypeChoices.TYPE_MULTISELECT:
-            filter_class = filters.MultiValueCharFilter
-            kwargs['lookup_expr'] = 'has_key'
+            filter_class = filters.MultiValueArrayFilter
 
         # Object
         elif self.type == CustomFieldTypeChoices.TYPE_OBJECT:
diff --git a/netbox/extras/tests/test_customfields.py b/netbox/extras/tests/test_customfields.py
index 7ac6b20358d..574452a81c5 100644
--- a/netbox/extras/tests/test_customfields.py
+++ b/netbox/extras/tests/test_customfields.py
@@ -1329,7 +1329,7 @@ def setUpTestData(cls):
 
         choice_set = CustomFieldChoiceSet.objects.create(
             name='Custom Field Choice Set 1',
-            extra_choices=(('a', 'A'), ('b', 'B'), ('c', 'C'), ('x', 'X'))
+            extra_choices=(('a', 'A'), ('b', 'B'), ('c', 'C'))
         )
 
         # Integer filtering
@@ -1435,7 +1435,7 @@ def setUpTestData(cls):
                 'cf7': 'http://a.example.com',
                 'cf8': 'http://a.example.com',
                 'cf9': 'A',
-                'cf10': ['A', 'X'],
+                'cf10': ['A', 'B'],
                 'cf11': manufacturers[0].pk,
                 'cf12': [manufacturers[0].pk, manufacturers[3].pk],
             }),
@@ -1449,7 +1449,7 @@ def setUpTestData(cls):
                 'cf7': 'http://b.example.com',
                 'cf8': 'http://b.example.com',
                 'cf9': 'B',
-                'cf10': ['B', 'X'],
+                'cf10': ['B', 'C'],
                 'cf11': manufacturers[1].pk,
                 'cf12': [manufacturers[1].pk, manufacturers[3].pk],
             }),
@@ -1463,7 +1463,7 @@ def setUpTestData(cls):
                 'cf7': 'http://c.example.com',
                 'cf8': 'http://c.example.com',
                 'cf9': 'C',
-                'cf10': ['C', 'X'],
+                'cf10': None,
                 'cf11': manufacturers[2].pk,
                 'cf12': [manufacturers[2].pk, manufacturers[3].pk],
             }),
@@ -1531,8 +1531,9 @@ def test_filter_select(self):
         self.assertEqual(self.filterset({'cf_cf9': ['A', 'B']}, self.queryset).qs.count(), 2)
 
     def test_filter_multiselect(self):
-        self.assertEqual(self.filterset({'cf_cf10': ['A', 'B']}, self.queryset).qs.count(), 2)
-        self.assertEqual(self.filterset({'cf_cf10': ['X']}, self.queryset).qs.count(), 3)
+        self.assertEqual(self.filterset({'cf_cf10': ['A']}, self.queryset).qs.count(), 1)
+        self.assertEqual(self.filterset({'cf_cf10': ['A', 'C']}, self.queryset).qs.count(), 2)
+        self.assertEqual(self.filterset({'cf_cf10': ['null']}, self.queryset).qs.count(), 1)
 
     def test_filter_object(self):
         manufacturer_ids = Manufacturer.objects.values_list('id', flat=True)
diff --git a/netbox/utilities/filters.py b/netbox/utilities/filters.py
index 1bf17beae32..72c9124a171 100644
--- a/netbox/utilities/filters.py
+++ b/netbox/utilities/filters.py
@@ -9,6 +9,7 @@
 __all__ = (
     'ContentTypeFilter',
     'MACAddressFilter',
+    'MultiValueArrayFilter',
     'MultiValueCharFilter',
     'MultiValueDateFilter',
     'MultiValueDateTimeFilter',
@@ -85,6 +86,21 @@ class MultiValueTimeFilter(django_filters.MultipleChoiceFilter):
     field_class = multivalue_field_factory(forms.TimeField)
 
 
+@extend_schema_field(OpenApiTypes.STR)
+class MultiValueArrayFilter(django_filters.MultipleChoiceFilter):
+    field_class = multivalue_field_factory(forms.CharField)
+
+    def __init__(self, *args, lookup_expr='contains', **kwargs):
+        # Set default lookup_expr to 'contains'
+        super().__init__(*args, lookup_expr=lookup_expr, **kwargs)
+
+    def get_filter_predicate(self, v):
+        # If filtering for null values, ignore lookup_expr
+        if v is None:
+            return {self.field_name: None}
+        return super().get_filter_predicate(v)
+
+
 class MACAddressFilter(django_filters.CharFilter):
     pass