EmailMessage utf-8 folding error

[andrzejQ]

BPO	45551
Nosy	@warsaw, @bitdancer, @andrzejQ
Files	ERROR_folding_in_EmailMessage.py: Missing white space after folding on ','

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-10-21.11:18:06.549>
labels = ['type-bug', 'expert-email', '3.9']
title = 'EmailMessage utf-8 folding error'
updated_at = <Date 2021-10-22.13:58:56.178>
user = 'https://github.com/andrzejQ'

bugs.python.org fields:

activity = <Date 2021-10-22.13:58:56.178>
actor = 'r.david.murray'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2021-10-21.11:18:06.549>
creator = 'andrzejQ'
dependencies = []
files = ['50380']
hgrepos = []
issue_num = 45551
keywords = []
message_count = 2.0
messages = ['404583', '404770']
nosy_count = 3.0
nosy_names = ['barry', 'r.david.murray', 'andrzejQ']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue45551'
versions = ['Python 3.9']

[andrzejQ]

email.message - EmailMessage Error
Missing white space after folding on ','

msg['To'] = 'Ab Ć<abc@def.com>,Ab Ć<abc@def.com>,Ab Ć<abc@def.com>,Ab Ć<abc@def.com>'

print(msg.as_string())
'''
To: Ab =?utf-8?q?=C4=86?=<abc@def.com>,Ab =?utf-8?q?=C4=86?=<abc@def.com>,
Ab =?utf-8?q?=C4=86?=<abc@def.com>,Ab =?utf-8?q?=C4=86?=<abc@def.com>
Subject: EmailMessage Error. Missing white space after folding on ",".
 https://www.ietf.org/rfc/rfc2822.txt , 2.2.3. Long Header Fields
'''

[bitdancer]

I'm pretty sure this is a duplicate report and that we worked on a fix, but I don't know if it got committed because I can't find the issue...

(To be clear, the problem here is the lack of whitespace at the start of the folded part of the header.)