# Buggy code
def _resolve_context(cli, prog_name, args):
    """Produce the context hierarchy starting with the command and
    traversing the complete arguments. This only follows the commands,
    it doesn't trigger input prompts or callbacks.

    :param cli: Command being called.
    :param prog_name: Name of the executable in the shell.
    :param args: List of complete args before the incomplete value.
    """
    ctx = cli.make_context(prog_name, args.copy(), resilient_parsing=True)
    args = ctx.protected_args + ctx.args

    while args:
        if isinstance(ctx.command, MultiCommand):
            if not ctx.command.chain:
                name, cmd, args = ctx.command.resolve_command(ctx, args)

                if cmd is None:
                    return ctx

                ctx = cmd.make_context(name, args, parent=ctx, resilient_parsing=True)
                args = ctx.protected_args + ctx.args
            else:
                while args:
                    name, cmd, args = ctx.command.resolve_command(ctx, args)

                    if cmd is None:
                        return ctx

                    sub_ctx = cmd.make_context(
                        name,
                        args,
                        parent=ctx,
                        allow_extra_args=True,
                        allow_interspersed_args=False,
                        resilient_parsing=True,
                    )
                    args = sub_ctx.args

                ctx = sub_ctx
                args = sub_ctx.protected_args + sub_ctx.args
        else:
            break

    return ctx


# Traceback (TypeError)
$ ./testclick subcommand <TAB>Traceback (most recent call last):
File "./testclick", line 23, in <module>
entrypoint(obj={'completions': ['abc', 'def', 'ghi', ]})
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/core.py", line 731, in __call__
return self.main(*args, **kwargs)
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/core.py", line 701, in main
_bashcomplete(self, prog_name, complete_var)
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/core.py", line 46, in _bashcomplete
if bashcomplete(cmd, prog_name, complete_var, complete_instr):
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/_bashcomplete.py", line 216, in bashcomplete
return do_complete(cli, prog_name)
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/_bashcomplete.py", line 205, in do_complete
for item in get_choices(cli, prog_name, args, incomplete):
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/_bashcomplete.py", line 186, in get_choices
ctx, all_args, incomplete, param))
File "/home/user/testclick/venv/lib/python3.6/site-packages/click/_bashcomplete.py", line 124, in get_user_autocompletions
incomplete=incomplete)
File "./testclick", line 7, in _complete
return ctx.obj['completions']
TypeError: 'NoneType' object is not subscriptable

# Fixed code
def _resolve_context(cli, ctx_args, prog_name, args):
    """Produce the context hierarchy starting with the command and
    traversing the complete arguments. This only follows the commands,
    it doesn't trigger input prompts or callbacks.

    :param cli: Command being called.
    :param prog_name: Name of the executable in the shell.
    :param args: List of complete args before the incomplete value.
    """
    ctx_args["resilient_parsing"] = True
    ctx = cli.make_context(prog_name, args.copy(), **ctx_args)
    args = ctx.protected_args + ctx.args

    while args:
        if isinstance(ctx.command, MultiCommand):
            if not ctx.command.chain:
                name, cmd, args = ctx.command.resolve_command(ctx, args)

                if cmd is None:
                    return ctx

                ctx = cmd.make_context(name, args, parent=ctx, resilient_parsing=True)
                args = ctx.protected_args + ctx.args
            else:
                while args:
                    name, cmd, args = ctx.command.resolve_command(ctx, args)

                    if cmd is None:
                        return ctx

                    sub_ctx = cmd.make_context(
                        name,
                        args,
                        parent=ctx,
                        allow_extra_args=True,
                        allow_interspersed_args=False,
                        resilient_parsing=True,
                    )
                    args = sub_ctx.args

                ctx = sub_ctx
                args = sub_ctx.protected_args + sub_ctx.args
        else:
            break

    return ctx