Not implemented error in built-in HTMLParser

from html.parser import HTMLParser
parser = HTMLParser()
parser.feed(bytearray.fromhex('3c215b63612121').decode('ascii'))

# This will throw (found by https://github.com/fuzzitdev/pythonfuzz):
Traceback (most recent call last):
  File "/Users/yevgenyp/fuzzitdev/pythonfuzz/pythonfuzz/fuzzer.py", line 21, in worker
    target(buf)
  File "examples/htmlparser/fuzz.py", line 12, in fuzz
    pass
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/html/parser.py", line 111, in feed
    self.goahead(0)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/html/parser.py", line 179, in goahead
    k = self.parse_html_declaration(i)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/html/parser.py", line 264, in parse_html_declaration
    return self.parse_marked_section(i)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/_markupbase.py", line 159, in parse_marked_section
    self.error('unknown status keyword %r in marked section' % rawdata[i+3:j])
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/_markupbase.py", line 34, in error
    "subclasses of ParserBase must override error()")
NotImplementedError: subclasses of ParserBase must override error()