Return a unicode object with the Gremlin representation of this BasicBlock.

def to_gremlin(self):
        """Return a unicode object with the Gremlin representation of this BasicBlock."""
        self.validate()
        if self.optional:
            operation = u'optional'
        else:
            operation = u'back'

        mark_name, _ = self.location.get_location_name()

        return u'{operation}({mark_name})'.format(
            operation=operation,
            mark_name=safe_quoted_string(mark_name))