Adding a new chart to sitecore Experience Analytics to show top search keywords which returns no result

Steps you need to follow:

1- Register "No search hits found" page event  in your service method when there is no result

https://doc.sitecore.net/sitecore_experience_platform/developing/marketing_operations/events/register_a_page_event_programmatically


2- Add  relevant dimension and segments

 http://sitecore-community.github.io/docs/xDB/reports/extending-experience-analytics-reports/