email.utils.encode_rfc2231(string, None, None) returns broken value

[spaceone]

BPO	40837
Nosy	@warsaw, @orsenthil, @bitdancer, @maxking, @spaceone
PRs	gh-85014: Fix email.utils.encode_rfc2231(string, None, None) #20564

^{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 2020-06-01.02:17:05.810>
labels = ['type-bug', 'library', 'expert-email', '3.10']
title = 'email.utils.encode_rfc2231(string, None, None) returns broken value'
updated_at = <Date 2020-06-05.04:08:13.869>
user = 'https://github.com/spaceone'

bugs.python.org fields:

activity = <Date 2020-06-05.04:08:13.869>
actor = 'xtreak'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'email']
creation = <Date 2020-06-01.02:17:05.810>
creator = 'spaceone'
dependencies = []
files = []
hgrepos = []
issue_num = 40837
keywords = []
message_count = 2.0
messages = ['370526', '370670']
nosy_count = 5.0
nosy_names = ['barry', 'orsenthil', 'r.david.murray', 'maxking', 'spaceone']
pr_nums = ['20564']
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40837'
versions = ['Python 3.10']

[spaceone]

encode_rfc2231() must not change the returned value if no transformation of the input was done.
This is also mentioned in the docstring of that function.

Actual behavior:
encode_rfc2231('foo bar', None, None)
'foo%20bar'

Expected behavior:
encode_rfc2231('foo bar', None, None)
'foo bar'

[orsenthil]

This will be a breaking change to the clients relying on current broken behavior, setting the fix version to 3.10 (current active).