[Plugin: Polylang] Error output before and "Headers already sent" error

The following error is displayed prior to html output on the page after activating the plugin:

Warning: in_array() expects parameter 2 to be array, null given in /path/to/wordpress/wp-content/plugins/polylang/include/core.php on line 330

Also, when unchecking “Hide URL language information for default language” in the language settings, the error also includes:

Warning: Cannot modify header information – headers already sent by (output started at /path/to/wordpress/wp-content/plugins/polylang/include/core.php:330) in /path/to/wordpress/wp-includes/pluggable.php on line 881

And, obviously, no html is output at all.

http://wordpress.org/extend/plugins/polylang/