You might see <empty search> in your Analytics if you are using a search-as-you-type solution such as Algolia's InstantSearch. In order to display results as soon as a user lands on the search page (and to speed-up future searches), Algolia performs a search with an empty query. Empty query searches show up in the Analytics as <empty search>.
You can exclude the empty search from your analytics if you want to, but please be aware that it can affect any analytical value for your app.