diff --git a/docs/release-notes/version-2.6.md b/docs/release-notes/version-2.6.md
index afad93fde..7d131ffc9 100644
--- a/docs/release-notes/version-2.6.md
+++ b/docs/release-notes/version-2.6.md
@@ -1,3 +1,11 @@
+# v2.6.10 (FUTURE)
+
+## Bug Fixes
+
+* [#3780](https://github.com/netbox-community/netbox/issues/3780) - Fix AttributeError exception in API docs
+
+---
+
 # v2.6.9 (2019-12-16)
 
 ## Enhancements
@@ -13,6 +21,8 @@
 * [#3749](https://github.com/netbox-community/netbox/issues/3749) - Fix exception on password change page for local users
 * [#3757](https://github.com/netbox-community/netbox/issues/3757) - Fix unable to assign IP to interface
 
+---
+
 # v2.6.8 (2019-12-10)
 
 ## Enhancements
@@ -35,6 +45,8 @@
 * [#3724](https://github.com/netbox-community/netbox/issues/3724) - Fix API filtering of interfaces by more than one device name
 * [#3725](https://github.com/netbox-community/netbox/issues/3725) - Enforce client validation for minimum service port number
 
+---
+
 # v2.6.7 (2019-11-01)
 
 ## Enhancements
diff --git a/netbox/extras/api/customfields.py b/netbox/extras/api/customfields.py
index 2a13e5ce1..e0c70efa3 100644
--- a/netbox/extras/api/customfields.py
+++ b/netbox/extras/api/customfields.py
@@ -124,6 +124,9 @@ class CustomFieldModelSerializer(ValidatedModelSerializer):
 
         else:
 
+            if not hasattr(self, 'initial_data'):
+                self.initial_data = {}
+
             # Populate default values
             if fields and 'custom_fields' not in self.initial_data:
                 self.initial_data['custom_fields'] = {}
diff --git a/netbox/utilities/tests/test_api.py b/netbox/utilities/tests/test_api.py
index 3ff4b3876..4aea682f4 100644
--- a/netbox/utilities/tests/test_api.py
+++ b/netbox/utilities/tests/test_api.py
@@ -1,7 +1,13 @@
+import urllib.parse
+
+from django.contrib.contenttypes.models import ContentType
+from django.test import Client, TestCase
 from django.urls import reverse
 from rest_framework import status
 
 from dcim.models import Region, Site
+from extras.constants import CF_TYPE_TEXT
+from extras.models import CustomField
 from ipam.models import VLAN
 from utilities.testing import APITestCase
 
@@ -117,3 +123,26 @@ class WritableNestedSerializerTest(APITestCase):
 
         self.assertHttpStatus(response, status.HTTP_400_BAD_REQUEST)
         self.assertEqual(VLAN.objects.count(), 0)
+
+
+class APIDocsTestCase(TestCase):
+
+    def setUp(self):
+        self.client = Client()
+
+        # Populate a CustomField to activate CustomFieldSerializer
+        content_type = ContentType.objects.get_for_model(Site)
+        self.cf_text = CustomField(type=CF_TYPE_TEXT, name='test')
+        self.cf_text.save()
+        self.cf_text.obj_type.set([content_type])
+        self.cf_text.save()
+
+    def test_api_docs(self):
+
+        url = reverse('api_docs')
+        params = {
+            "format": "openapi",
+        }
+
+        response = self.client.get('{}?{}'.format(url, urllib.parse.urlencode(params)))
+        self.assertEqual(response.status_code, 200)