I need to check when uploading PDF files to the media folder whether the file is, let's say, by checking the "author" file property. This is the code, I can't get the "author" property:

public class FileUploadEventHandler : INotificationHandler<MediaSavingNotification>
    {
        public void Handle(MediaSavingNotification notificatin)
        { 
                foreach (var media in notificatin.SavedEntities)
                {
                if (media.HasProperty("author"))
                    {
                        // Get the value of the property
                        var propertyValue = media.GetValue<string>("author");

                        // Perform your accessibility check here
                        if (!IsFileAccessible(propertyValue))
                        {
                        notificatin.CancelOperation(new EventMessage("error",
                            "The file is not accessible",
                            EventMessageType.Error));
                        // File is not accessible, prevent saving the media item
                      }
                    }                              
                }
            }
        private bool IsFileAccessible(string propertyValue)
        {
            // Implement your logic to check if the file is accessible
            // Return true if the file is accessible, otherwise return false
            // You can check permissions, file existence, file size, etc.
            // Based on your requirements

            // Example: Check if the property value is empty or null
            return !string.IsNullOrEmpty(propertyValue);
        }


    }