diff --git a/CHANGELOG.md b/CHANGELOG.md
index 49114a36..c60329ef 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@ any parts of the framework not mentioned in the documentation should generally b
 ### Fixed
 
 * Pass context from `PolymorphicModelSerializer` to child serializers to support fields which require a `request` context such as `url`.
+* Avoid patch on `RelationshipView` deleting relationship instance when constraint would allow null ([#242](https://github.com/django-json-api/django-rest-framework-json-api/issues/242))
 
 
 ## [2.6.0] - 2018-09-20
diff --git a/example/tests/test_views.py b/example/tests/test_views.py
index e4bf700f..5b778b90 100644
--- a/example/tests/test_views.py
+++ b/example/tests/test_views.py
@@ -11,7 +11,7 @@
 
 from . import TestBase
 from .. import views
-from example.factories import AuthorFactory, EntryFactory, CommentFactory
+from example.factories import AuthorFactory, CommentFactory, EntryFactory
 from example.models import Author, Blog, Comment, Entry
 from example.serializers import AuthorBioSerializer, AuthorTypeSerializer, EntrySerializer
 from example.views import AuthorViewSet
@@ -240,10 +240,14 @@ def test_new_comment_data_patch_to_many_relationship(self):
         previous_response = {
             'data': [
                 {'type': 'comments',
-                 'id': f'{self.second_comment.id}'
+                 'id': str(self.second_comment.id)
                  }
             ],
-            'links': {'self': f'http://testserver/authors/{self.author.id}/relationships/comment_set'}
+            'links': {
+                'self': 'http://testserver/authors/{}/relationships/comment_set'.format(
+                    self.author.id
+                )
+            }
         }
 
         response = self.client.get(url)
@@ -253,17 +257,21 @@ def test_new_comment_data_patch_to_many_relationship(self):
         new_patched_response = {
             'data': [
                 {'type': 'comments',
-                 'id': f'{comment.id}'
+                 'id': str(comment.id)
                  }
             ],
-            'links': {'self': f'http://testserver/authors/{self.author.id}/relationships/comment_set'}
+            'links': {
+                'self': 'http://testserver/authors/{}/relationships/comment_set'.format(
+                    self.author.id
+                )
+            }
         }
 
         response = self.client.patch(url, data=request_data)
         assert response.status_code == 200
         assert response.json() == new_patched_response
 
-        assert Comment.objects.filter(id=self.second_comment.id).exists
+        assert Comment.objects.filter(id=self.second_comment.id).exists()
 
 
 class TestRelatedMixin(APITestCase):
diff --git a/rest_framework_json_api/views.py b/rest_framework_json_api/views.py
index 224e4d8b..9f3178a1 100644
--- a/rest_framework_json_api/views.py
+++ b/rest_framework_json_api/views.py
@@ -254,7 +254,7 @@ def get(self, request, *args, **kwargs):
     def remove_relationships(self, instance_manager, field):
         field_object = getattr(instance_manager, field)
 
-        if getattr(field_object, "null"):
+        if field_object.null:
             for obj in instance_manager.all():
                 setattr(obj, field_object.name, None)
                 obj.save()
@@ -273,16 +273,15 @@ def patch(self, request, *args, **kwargs):
                 data=request.data, model_class=related_model_class, many=True
             )
             serializer.is_valid(raise_exception=True)
-            # related_instance_or_manager.all().delete()
 
             # for to one
             if hasattr(related_instance_or_manager, "field"):
-                related_instance_or_manager = self.remove_relationships(instance_manager=related_instance_or_manager,
-                                                                        field="field")
+                related_instance_or_manager = self.remove_relationships(
+                    instance_manager=related_instance_or_manager, field="field")
             # for to many
             else:
-                related_instance_or_manager = self.remove_relationships(instance_manager=related_instance_or_manager,
-                                                                        field="target_field")
+                related_instance_or_manager = self.remove_relationships(
+                    instance_manager=related_instance_or_manager, field="target_field")
 
             # have to set bulk to False since data isn't saved yet
             class_name = related_instance_or_manager.__class__.__name__