Alpine Linux 3.6 as VirtualBox Guest: Shared Folder package doesn't install

I'm trying to install the shared folder package as described in the wiki:

https://wiki.alpinelinux.org/wiki/VirtualBox_shared_folders

but when I type "apk add virtualbox-guest-modules-virthardened", I get the following result:

(1/1) Installing virtualbox-guest-modules-virthardened (4.9.37-r0)
Executing busybox-1.26.2-r5.trigger
depmod: can't open 'modules.builtin': No such file or directory
Executing kmod-23-r1.trigger
depmod: WARNING: could not open /lib/modules/4.9.37-0-virthardened/modules.order: No such file or directory
depmod: WARNING: could not open /lib/modules/4.9.37-0-virthardened/modules.builtin: No such file or directory

I have followed all the instructions written in this wiki:
https://wiki.alpinelinux.org/wiki/Install_Alpine_on_VirtualBox

So I'm not sure what I'm doing wrong.

As I am a newbie with Alpine, any help is appreciated.

Matt