system/Session/Session.php
public function getTempdata(string $key = null)
	{
		if (isset($key))
		{
			return (isset($_SESSION['__ci_vars'], $_SESSION['__ci_vars'][$key], $_SESSION[$key]) &&
					is_int($_SESSION['__ci_vars'][$key])) ? $_SESSION[$key] : null;
		}

		$tempdata = [];

		if (! empty($_SESSION['__ci_vars']))
		{
			foreach ($_SESSION['__ci_vars'] as $key => &$value)
			{
				is_int($value) && $tempdata[$key] = $_SESSION[$key];
			}
		}

		return $tempdata;
	}
public function getTempdata(string $key = null)
	{
		if (isset($key))
		{
			return (isset($_SESSION['__ci_vars'], $_SESSION['__ci_vars'][$key], $_SESSION[$key]) &&
					is_int($_SESSION['__ci_vars'][$key])) ? $_SESSION[$key] : null;
		}

		$tempdata = [];

		if (! empty($_SESSION['__ci_vars']))
		{
			foreach ($_SESSION['__ci_vars'] as $key => &$value)
			{
				is_int($value) && $tempdata[$key] = $_SESSION[$key];
			}
		}

		return $tempdata;
	}
Returns either a single piece of tempdata, or all temp data currently
in the session.

@param  string   $key   Session data key
@return mixed  Session data value or null if not found.