/// <summary>
/// Adds a game state instance to the game state map.
/// </summary>
/// <param name="state">The state instance.</param>
private void RegisterGameState(EngineState state)
{
if (state == null)
{
throw new ArgumentException("Cannot register a null state!");
}
StateId id = state.GetId();
_gameStates.Add(id, state);
}