Merge remote-tracking branch 'origin/master' into 2.4.0

Conflicts:
	.travis.yml
	docs/api-guide/fields.md
	docs/api-guide/routers.md
	docs/topics/release-notes.md
	rest_framework/authentication.py
	rest_framework/serializers.py
	rest_framework/templatetags/rest_framework.py
	rest_framework/tests/test_authentication.py
	rest_framework/tests/test_filters.py
	rest_framework/tests/test_hyperlinkedserializers.py
	rest_framework/tests/test_serializer.py
	rest_framework/tests/test_testing.py
	rest_framework/utils/encoders.py
	tox.ini

1 files changed, 8 insertions, 0 deletions

diff --git a/rest_framework/tests/serializers.py b/rest_framework/tests/serializers.py
new file mode 100644
index 00000000..cc943c7d
--- /dev/null
+++ b/rest_framework/tests/serializers.py
@@ -0,0 +1,8 @@
+from rest_framework import serializers
+
+from rest_framework.tests.models import NullableForeignKeySource
+
+
+class NullableFKSourceSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = NullableForeignKeySource