From 04ee55a40cc25ed09238c538f2eb5b7b8dfa4858 Mon Sep 17 00:00:00 2001
From: Jeremy Stretch <stretch@packetlife.net>
Date: Fri, 21 Feb 2020 21:38:25 -0500
Subject: [PATCH] Fixes #4240: Fix exception when filtering foreign keys by
 NULL

---
 docs/release-notes/version-2.7.md |  1 +
 netbox/utilities/forms.py         | 16 ++++++++--------
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/docs/release-notes/version-2.7.md b/docs/release-notes/version-2.7.md
index 26ba370bd..be45c9846 100644
--- a/docs/release-notes/version-2.7.md
+++ b/docs/release-notes/version-2.7.md
@@ -11,6 +11,7 @@
 * [#4232](https://github.com/netbox-community/netbox/issues/4232) - Enforce consistent background striping in rack elevations
 * [#4235](https://github.com/netbox-community/netbox/issues/4235) - Fix API representation of `content_type` for export templates
 * [#4239](https://github.com/netbox-community/netbox/issues/4239) - Fix exception when selecting all filtered objects during bulk edit
+* [#4240](https://github.com/netbox-community/netbox/issues/4240) - Fix exception when filtering foreign keys by NULL
 
 ---
 
diff --git a/netbox/utilities/forms.py b/netbox/utilities/forms.py
index a7ee63eaa..71c262cdc 100644
--- a/netbox/utilities/forms.py
+++ b/netbox/utilities/forms.py
@@ -2,8 +2,9 @@ import csv
 import json
 import re
 from io import StringIO
-import yaml
 
+import django_filters
+import yaml
 from django import forms
 from django.conf import settings
 from django.contrib.postgres.forms.jsonb import JSONField as _JSONField, InvalidJSONInput
@@ -564,18 +565,17 @@ class TagFilterField(forms.MultipleChoiceField):
 
 
 class DynamicModelChoiceMixin:
-    field_modifier = ''
+    filter = django_filters.ModelChoiceFilter
 
     def get_bound_field(self, form, field_name):
         bound_field = BoundField(form, self, field_name)
 
         # Modify the QuerySet of the field before we return it. Limit choices to any data already bound: Options
         # will be populated on-demand via the APISelect widget.
-        field_name = '{}{}'.format(self.to_field_name or 'pk', self.field_modifier)
-        if bound_field.data:
-            self.queryset = self.queryset.filter(**{field_name: self.prepare_value(bound_field.data)})
-        elif bound_field.initial:
-            self.queryset = self.queryset.filter(**{field_name: self.prepare_value(bound_field.initial)})
+        data = bound_field.data or bound_field.initial
+        if data:
+            filter = self.filter(field_name=self.to_field_name or 'pk', queryset=self.queryset)
+            self.queryset = filter.filter(self.queryset, data)
         else:
             self.queryset = self.queryset.none()
 
@@ -594,7 +594,7 @@ class DynamicModelMultipleChoiceField(DynamicModelChoiceMixin, forms.ModelMultip
     """
     A multiple-choice version of DynamicModelChoiceField.
     """
-    field_modifier = '__in'
+    filter = django_filters.ModelMultipleChoiceFilter
 
 
 class LaxURLField(forms.URLField):