package node type Nullable struct { Expr Node } func NewNullable(Expression Node) *Nullable { return &Nullable{ Expression, } } func (n *Nullable) Attributes() map[string]interface{} { return nil } func (n *Nullable) Walk(v Visitor) { if v.EnterNode(n) == false { return } if n.Expr != nil { vv := v.GetChildrenVisitor("Expr") n.Expr.Walk(vv) } v.LeaveNode(n) }