Empty settings should also be coerced to lists. Closes #3087.

rest_framework/settings.py

@@ -204,7 +204,7 @@ class APISettings(object):
             val = self.defaults[attr]
 
         # Coerce import strings into classes
-        if val and attr in self.import_strings:
+        if attr in self.import_strings:
             val = perform_import(val, attr)
 
         # Cache the result

tests/test_settings.py

@@ -17,3 +17,16 @@ class TestSettings(TestCase):
         })
         with self.assertRaises(ImportError):
             settings.DEFAULT_RENDERER_CLASSES
+
+
+class TestSettingTypes(TestCase):
+    def test_settings_consistently_coerced_to_list(self):
+        settings = APISettings({
+            'DEFAULT_THROTTLE_CLASSES': ('rest_framework.throttling.BaseThrottle',)
+        })
+        self.assertTrue(isinstance(settings.DEFAULT_THROTTLE_CLASSES, list))
+
+        settings = APISettings({
+            'DEFAULT_THROTTLE_CLASSES': ()
+        })
+        self.assertTrue(isinstance(settings.DEFAULT_THROTTLE_CLASSES, list))