# Buggy code
def match(
    self,
    segments,
    match_depth=0,
    parse_depth=0,
    verbosity=0,
    dialect=None,
    match_segment=None,
):
    elem = self._get_elem(dialect=dialect)

    if elem:
        # Match against that. NB We're not incrementing the match_depth here.
        # References shouldn't relly count as a depth of match.
        match_segment = self._get_ref()
        return elem._match(
            segments=segments,
            match_depth=match_depth,
            parse_depth=parse_depth,
            verbosity=verbosity,
            dialect=dialect,
            match_segment=match_segment,
        )
    else:
        raise ValueError(
            "Null Element returned! _elements: {0!r}".format(self._elements)
        )


# Traceback (TypeError)
Traceback (most recent call last):
File "/home/user/sql/.venv/bin/sqlfluff", line 11, in <module>
load_entry_point('sqlfluff==0.1.3', 'console_scripts', 'sqlfluff')()
File "/home/user/sql/.venv/lib/python3.7/site-packages/click/core.py", line 764, in __call__
return self.main(*args, **kwargs)
File "/home/user/sql/.venv/lib/python3.7/site-packages/click/core.py", line 717, in main
rv = self.invoke(ctx)
File "/home/user/sql/.venv/lib/python3.7/site-packages/click/core.py", line 1137, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/home/user/sql/.venv/lib/python3.7/site-packages/click/core.py", line 956, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/home/user/sql/.venv/lib/python3.7/site-packages/click/core.py", line 555, in invoke
return callback(*args, **kwargs)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/cli/commands.py", line 85, in lint
result = lnt.lint_paths(paths, verbosity=verbose)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/linter.py", line 324, in lint_paths
result.add(self.lint_path(path, verbosity=verbosity, fix=fix))
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/linter.py", line 312, in lint_path
linted_path.add(self.lint_file(f, fname=fname, verbosity=verbosity, fix=fix))
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/linter.py", line 212, in lint_file
parsed, vs, time_dict = self.parse_file(f=f, fname=fname, verbosity=verbosity)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/linter.py", line 193, in parse_file
parsed = fs.parse(recurse=recurse, verbosity=verbosity, dialect=self.dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 228, in parse
verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 394, in expand
res = stmt.parse(recurse=recurse, parse_depth=parse_depth, verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 228, in parse
verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 394, in expand
res = stmt.parse(recurse=recurse, parse_depth=parse_depth, verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 228, in parse
verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 394, in expand
res = stmt.parse(recurse=recurse, parse_depth=parse_depth, verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 228, in parse
verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 394, in expand
res = stmt.parse(recurse=recurse, parse_depth=parse_depth, verbosity=verbosity, dialect=dialect)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 186, in parse
dialect=dialect, match_segment=self.__class__.__name__)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 70, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 273, in match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 70, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 485, in match
match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 70, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 273, in match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 70, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 236, in match
dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 361, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/segments_base.py", line 320, in match
dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 70, in _match
verbosity=verbosity, dialect=dialect, match_segment=match_segment)
File "/home/user/sql/.venv/lib/python3.7/site-packages/sqlfluff/parser/grammar.py", line 586, in match
segment=segments[start_bracket_idx])
TypeError: tuple indices must be integers or slices, not NoneType

# Fixed code
def match(self, segments, parse_context):
    elem = self._get_elem(dialect=parse_context.dialect)

    if elem:
        # Match against that. NB We're not incrementing the match_depth here.
        # References shouldn't relly count as a depth of match.
        return elem._match(
            segments=segments,
            parse_context=parse_context.copy(match_segment=self._get_ref()),
        )
    else:
        raise ValueError(
            "Null Element returned! _elements: {0!r}".format(self._elements)
        )