For omitempty to work properly, nested structs have to be pointers

api/get_indexes.go

@@ -62,6 +62,6 @@ func (c *GetIndexesController) Get() {
 	}
 
 	response := responses.NewEmpty()
-	response.ArtistIndex = res
+	response.ArtistIndex = &res
 	c.Ctx.Output.Body(responses.ToXML(response))
 }

api/get_license.go

@@ -9,7 +9,7 @@ type GetLicenseController struct{ beego.Controller }
 
 func (c *GetLicenseController) Get() {
 	response := responses.NewEmpty()
-	response.License = responses.License{Valid: true}
+	response.License = &responses.License{Valid: true}
 
 	c.Ctx.Output.Body(responses.ToXML(response))
 }

api/get_music_folders.go

@@ -25,6 +25,6 @@ func (c *GetMusicFoldersController) Get() {
 		folders[i].Name = f.Name
 	}
 	response := responses.NewEmpty()
-	response.MusicFolders = responses.MusicFolders{Folders: folders}
+	response.MusicFolders = &responses.MusicFolders{Folders: folders}
 	c.Ctx.Output.Body(responses.ToXML(response))
 }

api/responses/responses.go

@@ -7,9 +7,9 @@ type Subsonic struct {
 	Status       string   `xml:"status,attr"`
 	Version      string   `xml:"version,attr"`
 	Body         []byte   `xml:",innerxml"`
-	License      License  `xml:",omitempty"`
-	MusicFolders MusicFolders `xml:",omitempty"`
-	ArtistIndex  ArtistIndex `xml:",omitempty"`
+	License      *License  `xml:",omitempty"`
+	MusicFolders *MusicFolders `xml:",omitempty"`
+	ArtistIndex  *ArtistIndex `xml:",omitempty"`
 }
 
 type License struct {