def add_breadcrumb(self, *args, **kwargs):
        """Adds a breadcrumb."""
        client, scope = self._stack[-1]
        if client is None:
            logger.info("Dropped breadcrumb because no client bound")
            return

        if len(args) == 2:
            crumb, hint = args
        elif len(args) == 1:
            crumb = args[0] or {}
            hint = kwargs.pop("hint", None)
            crumb.update(kwargs)
        elif kwargs:
            hint = kwargs.pop("hint", None)
            crumb = kwargs

        if crumb is None:
            return

        if crumb.get("timestamp") is None:
            crumb["timestamp"] = datetime.utcnow()
        if crumb.get("type") is None:
            crumb["type"] = "default"

        original_crumb = crumb
        if client.options["before_breadcrumb"] is not None:
            crumb = client.options["before_breadcrumb"](crumb, hint)

        if crumb is not None:
            scope._breadcrumbs.append(crumb)
        else:
            logger.info("before breadcrumb dropped breadcrumb (%s)", original_crumb)
        while len(scope._breadcrumbs) >= client.options["max_breadcrumbs"]:
            scope._breadcrumbs.popleft()