check image for null safety

lib/pages/widgets/multi_img_controller.dart

@@ -5,12 +5,12 @@ import 'display_image_source.dart';
 
 class MultiImgController {
   List<String> imageUrls = [];
-  List<File> imageFiles = [];
+  List<File?> imageFiles = [];
   List<DisplayImageSource> addedFiles = [];
   List<DisplayImageSource> removedFiles = [];
 
   List<DisplayImageSource> fileContainers = [];
-  CallBack callback;
+  CallBack? callback;
   MultiImgController() {
     fileContainers = [];
   }
@@ -26,7 +26,7 @@ class MultiImgController {
       fileContainers.add(DisplayImageSource(url: e));
     });
     if (callback != null) {
-      callback();
+      callback!();
     }
   }
 
@@ -42,7 +42,7 @@ class MultiImgController {
       fileContainers.add(DisplayImageSource(file: e));
     });
     if (callback != null) {
-      callback();
+      callback!();
     }
   }
 
@@ -54,7 +54,7 @@ class MultiImgController {
     // if (fileContainers.contains(fileContainer)) return;
     addedFiles.add(fileContainer);
     if (callback != null) {
-      callback();
+      callback!();
     }
   }
 
@@ -74,11 +74,11 @@ class MultiImgController {
     }
 
     if (callback != null) {
-      callback();
+      callback!();
     }
   }
 
-  List<File> get getUpdatedFile {
+  List<File?> get getUpdatedFile {
     List<File?> _addfiles = getAddedFile;
     this.imageFiles.addAll(_addfiles);
     return this.imageFiles;