func (s *Series) GetExpression() string {
	if s == nil || s.Expression == nil {
		return ""
	}
	return *s.Expression
}
func (s *Series) GetExpression() string {
	if s == nil || s.Expression == nil {
		return ""
	}
	return *s.Expression
}
// GetExpression returns the Expression field if non-nil, zero value otherwise.