code: func (c *Connector) Upsert(ctx context.Context, ei *dosa.EntityInfo, values map[string]dosa.FieldValue) error {
  	if c.Next == nil {
  		return NewErrNoMoreConnector()
  	}
  	return c.Next.Upsert(ctx, ei, values)
  }
docs: // Upsert calls Next