urllib.parse.unquote_plus raises incorrect error message when string parameter is bytes

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-10-23.17:45:50.619>
labels = ['library', '3.9']
title = 'urllib.parse.unquote_plus raises incorrect error message when string parameter is bytes'
updated_at = <Date 2020-01-10.22:26:27.729>
user = 'https://github.com/stein-k'

bugs.python.org fields:

activity = <Date 2020-01-10.22:26:27.729>
actor = 'cheryl.sabella'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-10-23.17:45:50.619>
creator = 'stein-k'
dependencies = []
files = []
hgrepos = []
issue_num = 38567
keywords = ['patch']
message_count = 1.0
messages = ['355242']
nosy_count = 3.0
nosy_names = ['orsenthil', 'eamanu', 'stein-k']
pr_nums = ['16903']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue38567'
versions = ['Python 3.9']