[API] search for keywords in title returns empty results

```
search_results = impresso_session.search.find(
    title="Berlin",
    order_by="-date",
    limit=20
)
```

Expected: A dataframe with content items where title contains keyphrase "Berlin"

Returned: Empty 

I also tested with other keywords including "Thief" and "Dieb" (smaller and uppercase), and without the order_by. Always empty result.