Of course, since the DOJ has subsequently provided numerous documents which include email traffic with various FBI officials (see: FOIA Dump Reveals Collusion Between Lynch, FBI And Media To Bury Bill Clinton Meeting), we now know that the FBI's original response was either (i) just a simple reflection of their complete incompetence (best case) or (ii) an outright lie (worst case).

Alas, it seems as though the FBI has finally admitted in a new letter sent to Sekulow that maybe, just maybe, there are "records potentially responsive to your request" and, as such, they've 'reopened' the case to search for those records.  

"...your request has been reopened under the FOIPA number listed above as the FBI has determined records potentially responsive to your request may exist.  We are currently in the process of searching for any responsive material."