search_api_db_search_index_search_api_language does not have a primary key

I got message:
For this to work correctly, all tables must have a primary key. The following table(s) do not have a primary key: search_api_db_fulltext_1.

What I did was custom update_hook for custom module.install file

function mymodule_update_10001() {
  \Drupal::database()->schema()->addPrimaryKey('search_api_db_fulltext_1', ['item_id']);
}

This seems to be a result of some previous error when first creating the search index. Normally, that table should have a primary key.
Unless you can reproduce this problem from a new installation, please just add the primary key (on item_id, value) manually.