func (e *IsNull) IsNullable() bool {
	return false
}
IsNullable implements the Expression interface.
package expression
import "github.com/src-d/go-mysql-server/sql"
type IsNull struct {
	UnaryExpression
}
func NewIsNull(child sql.Expression) *IsNull {
	return &IsNull{UnaryExpression{child}}
}
func (e *IsNull) Type() sql.Type {
	return sql.Boolean
}