Why does an error appear when searching in the default WordPress search template?

Question

WordPress

I took the search.php, content-search.php, content-none.php files from the base WordPress theme (for example, from twentyfifteen) and copied them into my theme in the hope that everything would work. But in the end, it constantly displays content-none.php for me, because it doesn’t seem to find anything. But if you do not drive anything into the search and click "search", then it gives me the following error:

I just copied these files, did not change anything.

Answer 1

The twentyfifteen_post_thumbnail function is not defined in your theme , which is called in the c content-search.php file