add optional "hideIfEmpty" parameter in "listAlbums" API to show empty albums, only available on iOS platform

ios/Classes/SwiftPhotoGalleryPlugin.swift

@@ -15,7 +15,8 @@ public class SwiftPhotoGalleryPlugin: NSObject, FlutterPlugin {
     if(call.method == "listAlbums") {
       let arguments = call.arguments as! Dictionary<String, AnyObject>
       let mediumType = arguments["mediumType"] as! String
-      result(listAlbums(mediumType: mediumType))
+      let hideIfEmpty = arguments["hideIfEmpty"] as? Bool
+      result(listAlbums(mediumType: mediumType, hideIfEmpty: hideIfEmpty))
     }
     else if(call.method == "listMedia") {
       let arguments = call.arguments as! Dictionary<String, AnyObject>
@@ -89,7 +90,7 @@ public class SwiftPhotoGalleryPlugin: NSObject, FlutterPlugin {
   
   private var assetCollections : [PHAssetCollection]  = []
   
-  private func listAlbums(mediumType: String) -> [NSDictionary] {
+  private func listAlbums(mediumType: String, hideIfEmpty: Bool? = true) -> [NSDictionary] {
     self.assetCollections = []
     let fetchOptions = PHFetchOptions()
     var total = 0
@@ -142,13 +143,13 @@ public class SwiftPhotoGalleryPlugin: NSObject, FlutterPlugin {
     // Smart Albums.
     processPHAssetCollections(
       fetchResult: PHAssetCollection.fetchAssetCollections(with: .smartAlbum, subtype: .albumRegular, options: fetchOptions),
-      hideIfEmpty: true
+      hideIfEmpty: hideIfEmpty ?? true
     )
     
     // User-created collections.
     processPHCollections(
       fetchResult: PHAssetCollection.fetchTopLevelUserCollections(with: fetchOptions),
-      hideIfEmpty: true
+      hideIfEmpty: hideIfEmpty ?? true
     )
     
     albums.insert([

lib/photo_gallery.dart

@@ -25,9 +25,11 @@ class PhotoGallery {
   /// List all available gallery albums and counts number of items of [MediumType].
   static Future<List<Album>> listAlbums({
     required MediumType mediumType,
+    bool? hideIfEmpty = true,
   }) async {
     final json = await _channel.invokeMethod('listAlbums', {
       'mediumType': mediumTypeToJson(mediumType),
+      'hideIfEmpty': hideIfEmpty
     });
     return json.map<Album>((x) => Album.fromJson(x)).toList();
   }
@@ -78,6 +80,7 @@ class PhotoGallery {
       'height': height,
       'highQuality': highQuality,
     });
+    if (bytes == null) throw "Failed to fetch thumbnail of medium $mediumId";
     return new List<int>.from(bytes);
   }
 
@@ -96,6 +99,7 @@ class PhotoGallery {
       'height': height,
       'highQuality': highQuality,
     });
+    if (bytes == null) throw "Failed to fetch thumbnail of album $albumId";
     return new List<int>.from(bytes);
   }