public Dictionary<int, Dictionary<int, bool?>> PermissionsData { get; set; }

 public void Combine(IPermission p) {
  // ...... some logic
     if (p == null)
        return;

      TypePermission otherP = (TypePermission)p;

      foreach (int objId in otherP.PermissionsData.Keys)
      {
        if (PermissionsData.ContainsKey(objId))
          CombineEntityPerms(objId, otherP.PermissionsData[objId]);
        else
          PermissionsData.Add(objId, otherP.PermissionsData[objId]);
      }
// some logic...
}