func (c *conn) CheckNamedValue(nv *driver.NamedValue) error {
	switch nv.Value.(type) {
	case Lob, *Lob:
		nv.Value = nil
	}
	return nil
}
func (c *conn) CheckNamedValue(nv *driver.NamedValue) error {
	switch nv.Value.(type) {
	case Lob, *Lob:
		nv.Value = nil
	}
	return nil
}
// CheckNamedValue implements NamedValueChecker interface.
// implemented for conn:
// if querier or execer is called, sql checks parameters before
// in case of parameters the method can be 'skipped' and force the prepare path
// --> guarantee that a valid driver value is returned
// --> if not implemented, Lob need to have a pseudo Value method to return a valid driver value