email message get_content throws KeyError for content main types font and model

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-10-16.19:24:02.400>
labels = ['3.7', '3.8', '3.9', '3.10']
title = 'email message get_content throws KeyError for content main types font and model'
updated_at = <Date 2020-10-16.19:24:02.400>
user = 'https://github.com/msapiro'

bugs.python.org fields:

activity = <Date 2020-10-16.19:24:02.400>
actor = 'msapiro'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2020-10-16.19:24:02.400>
creator = 'msapiro'
dependencies = []
files = []
hgrepos = []
issue_num = 42054
keywords = []
message_count = 1.0
messages = ['378738']
nosy_count = 1.0
nosy_names = ['msapiro']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue42054'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']