fix(prepared) descriptive errors and nil query id catch

src/cassandra.lua

@@ -757,7 +757,7 @@ local function prepare_query(request_handler, query)
     local prepared_key_lock = prepared_key.."_lock"
     local lock, lock_err, elapsed = lock_mutex(request_handler.options.prepared_shm, prepared_key_lock)
     if lock_err then
-      return nil, lock_err
+      return nil, "Could not create lock for prepare request: "..lock_err
     end
 
     if elapsed and elapsed == 0 then
@@ -767,26 +767,30 @@ local function prepare_query(request_handler, query)
       local res, err = request_handler:send(prepare_request)
       if err then
         return nil, err
+      elseif res.query_id == nil then
+        return nil, "Could not retrieve query id from prepare request"
       end
       query_id = res.query_id
       local ok, cache_err = cache.set_prepared_query_id(request_handler.options, query, query_id)
       if not ok then
-        return nil, cache_err
+        return nil, "Could not insert query id in cache for prepared query: "..cache_err
       end
       log.info("Query prepared for host "..request_handler.coordinator.address)
     else
       -- once the lock is resolved, all other workers can retry to get the query, and should
       -- instantly succeed. We then skip the preparation part.
       query_id, cache_err = cache.get_prepared_query_id(request_handler.options, query)
       if cache_err then
-        return nil, cache_err
+        return nil, "Could not get query id from cache for prepared query: "..cache_err
+      elseif query_id == nil then
+        return nil, "No query id found in cache for prepared query"
       end
     end
 
     -- UNLOCK MUTEX
     lock_err = unlock_mutex(lock)
     if lock_err then
-      return nil, "Error unlocking mutex for query preparation: "..lock_err
+      return nil, "Error unlocking mutex for query for prepare request: "..lock_err
     end
   end