id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
33458	Messages framework incorrectly serializes/deserializes extra_tags when it's an empty string	Tim McCurrach	Tim McCurrach	"When a message is serialised and then deserialised with any of the built in storage backends, then `extra_tags==""""` is converted to `extra_tags==None`. This is because `MessageEncoder` checks for the truthyness of `extra_tags` rather than checking it is not `None`.

=== To replicate this bug ===

{{{
>>> from django.conf import settings
>>> settings.configure()  # Just to allow the following import
>>> from django.contrib.messages.storage.base import Message
>>> from django.contrib.messages.storage.cookie import MessageEncoder, MessageDecoder
>>> original_message = Message(10, ""Here is a message"", extra_tags="""")
>>> encoded_message = MessageEncoder().encode(original_message)
>>> decoded_message = MessageDecoder().decode(encoded_message)
>>> original_message.extra_tags == """"
True
>>> decoded_message.extra_tags is None
True
}}}

=== Effect of the bug in application behaviour ===
This error occurred in the wild with a template tag similar to the following:
{{{
{% if x not in message.extra_tags %}
}}}
When the message was displayed as part of a redirect, it had been serialised and deserialized which meant that extra_tags was `None` instead of the empty string. This caused an error.

It's important to note that this bug affects all of the standard API (`messages.debug`, `messages.info` etc. all have a default value of `extra_tags` equal to `""""`)."	Bug	closed	contrib.messages	4.0	Normal	fixed			Ready for checkin	1	0	0	0	0	0