By default, the Search Portlets do not execute a search if they have no keywords. Even if they sent the request, the framework returns no result if no keyword is given.
However, there are use cases for returning all elements when executing a query without keywords. This mode, called "keyword-free search," is useful, for example, in Commerce, where the first access to a search page should list all results possible (ranked by other means) if there is no query.
So, we have to implement it. We need to add a setting to some search portlet (maybe Search Results) enabling that, and also add a new flag to SearchContext which, when set, returns all results for the query, instead of returning none.