How to add permissions to a file or folder on Google drive in C#

Google drive insert permissions Csharp

/// <summary>
  /// Insert a new permission.
  /// </summary>
  /// <param name="service">Drive API service instance.</param>
  /// <param name="fileId">ID of the file to insert permission for.</param>
  /// <param name="who">
  /// User or group e-mail address, domain name or null for "default" type.
  /// </param>
  /// <param name="type">The value "user", "group", "domain" or "default".</param>
  /// <param name="role">The value "owner", "writer" or "reader".</param>
  /// <returns>The inserted permission, null is returned if an API error occurred</returns>
  public static Permission InsertPermission(DriveService service, String fileId, String who,String type, String role) {
    Permission newPermission = new Permission();
    newPermission.Value = value;
    newPermission.Type = type;
    newPermission.Role = role;
    try {
      return service.Permissions.Insert(newPermission, fileId).Execute();
    } catch (Exception e) {
      Console.WriteLine("An error occurred: " + e.Message);
    }
    return null;
  }

It is just returning null.