render empty oauth scopes

see https://github.com/pb33f/libopenapi/issues/289

datamodel/high/node_builder.go

@@ -429,7 +429,7 @@ func (n *NodeBuilder) AddYAMLNode(parent *yaml.Node, entry *nodes.NodeEntry) *ya
 			}
 
 			p := m.ToYamlNode(n, l)
-			if len(p.Content) > 0 {
+			if p.Content != nil {
 				valueNode = p
 			}
 		} else if r, ok := value.(Renderable); ok {

datamodel/high/v3/oauth_flow.go

@@ -16,7 +16,7 @@ type OAuthFlow struct {
 	AuthorizationUrl string                              `json:"authorizationUrl,omitempty" yaml:"authorizationUrl,omitempty"`
 	TokenUrl         string                              `json:"tokenUrl,omitempty" yaml:"tokenUrl,omitempty"`
 	RefreshUrl       string                              `json:"refreshUrl,omitempty" yaml:"refreshUrl,omitempty"`
-	Scopes           *orderedmap.Map[string, string]     `json:"scopes,omitempty" yaml:"scopes,omitempty"`
+	Scopes           *orderedmap.Map[string, string]     `json:"scopes,renderZero" yaml:"scopes,renderZero"`
 	Extensions       *orderedmap.Map[string, *yaml.Node] `json:"-" yaml:"-"`
 	low              *low.OAuthFlow
 }

orderedmap/builder.go

@@ -36,6 +36,9 @@ type findValueUntyped interface {
 // ToYamlNode converts the ordered map to a yaml node ready for marshalling.
 func (o *Map[K, V]) ToYamlNode(n NodeBuilder, l any) *yaml.Node {
 	p := utils.CreateEmptyMapNode()
+	if o != nil {
+		p.Content = make([]*yaml.Node, 0)
+	}
 
 	var vn *yaml.Node