public static function instance( $set = null ) 
	{
		if ( is_null( $set ) ) 
		{
			return static::$_instance;
		}
		
		if ( !$set instanceof CCIn_Instance ) 
		{
			throw new \InvalidArgumentException('CCIn::set() - only CCIn_Instance object can be passed.');
		}
		
		static::$_instance = $set;
	}