Only set .action attribute in override_method if it already existed on the view

rest_framework/request.py

@@ -46,13 +46,16 @@ class override_method(object):
 
     def __enter__(self):
         self.view.request = clone_request(self.request, self.method)
+        if self.action is not None:
+            # For viewsets we also set the `.action` attribute.
             action_map = getattr(self.view, 'action_map', {})
             self.view.action = action_map.get(self.method.lower())
         return self.view.request
 
     def __exit__(self, *args, **kwarg):
-        self.view.action = self.action
         self.view.request = self.request
+        if self.action is not None:
+            self.view.action = self.action
 
 
 class Empty(object):