When accessing /content/history/<node_id> with PHP Notices display enabled, an error Array to string conversion is shown for each displayed version.

This is because of the usage of array_unique() which is not intended to be used on multi-dimensional array (see http://php.net/array_unique in the "Notes" section).

array_unique() performs differently under different PHP versions. Please have a look at http://3v4l.org/jvZbD to see how the different PHP versions are affected.

The array I used there is an actual version array we have in our project.