cache: handle stale list result

src/cache.rs

@@ -86,8 +86,16 @@ impl DnsCache {
             ));
         }
 
+        if ret.len() == 0 {
+            // Sometimes the KV list operation may return stale keys that
+            // are no longer valid, resulting in we skipping over them in
+            // the main loop above. This could result in a non-empty
+            // keys array but an empty return value.
+            None
+        } else {
             Some(ret)
         }
+    }
 
     fn record_to_key(record: &Record<Dname<Vec<u8>>, OwnedRecordData>, buf: &[u8]) -> String {
         format!(