inspect.findsource breaks on class frame objects

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-10-29.04:17:50.821>
labels = ['3.7', '3.8', 'type-bug', 'library']
title = 'inspect.findsource breaks on class frame objects'
updated_at = <Date 2019-01-26.06:52:01.121>
user = 'https://github.com/orlnub123'

bugs.python.org fields:

activity = <Date 2019-01-26.06:52:01.121>
actor = 'Aivar.Annamaa'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2018-10-29.04:17:50.821>
creator = 'orlnub123'
dependencies = []
files = []
hgrepos = []
issue_num = 35101
keywords = ['patch']
message_count = 3.0
messages = ['328788', '328800', '329033']
nosy_count = 4.0
nosy_names = ['Aivar.Annamaa', 'yselivanov', 'xtreak', 'orlnub123']
pr_nums = ['10209']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue35101'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']