Trigger to execute just before closing the span

        :param opentracing.span.Span  span: the SpanContext instance
        :param Any obj: Object to use as context
        :param dict kwargs: additional data

def _postrun(cls, span, obj, **kwargs):
        """ Trigger to execute just before closing the span

        :param opentracing.span.Span  span: the SpanContext instance
        :param Any obj: Object to use as context
        :param dict kwargs: additional data
        """
        for key, value in ResultSchema().dump(obj.result).items():
            if isinstance(value, dict):
                try:
                    flat_data = cls.filter_keys(
                        cls.fix_additional_fields(value)
                    )
                    span.set_tag("result.{}".format(key), json.dumps(flat_data))
                except Exception:
                    span.set_tag("result.{}".format(key), "N/A")
            elif isinstance(value, (list, tuple)):
                try:
                    span.set_tag("result.{}".format(key), json.dumps(value))
                except Exception:
                    try:
                        span.set_tag("result.{}".format(key), value)
                    except Exception:
                        span.set_tag("result.{}".format(key), "N/A")
            else:
                span.set_tag("result.{}".format(key), value)