[Koha] First catalog, first search failed

[Narcis Garcia]

MyLibrary-intra.example.net
Once I've defined a (I hope) final framework to work with, I've
catalogued a first book. I didn't add any "item".

Just after this, I've visited OPAC at ~ MyLibrary.example.net and filled
search textbox with author's name -> [Go]
The answer is:

You did not specify any search criteria
No results found!
You did not specify any search criteria.
Error:
Could not find opac-search.xml in /usr/share/koha/opac/cgi-bin/opac/ at
/usr/share/koha/lib/C4/Search.pm line 871.

What have I missed to do for this Koha 17.11 setup?

Thanks.