fix query cache

Author: amuluowin

src/Command.php

@@ -154,7 +154,7 @@ protected function queryInternal($method, $fetchMode = null)
                     $this->db->dsn,
                     $rawSql,
                 ]);
-                if (false !== $ret = $cache->get((string)$cacheKey)) {
+                if (!empty($ret = $cache->get($cacheKey))) {
                     $result = unserialize($ret);
                     if (is_array($result) && isset($result[0])) {
                         $this->logQuery($rawSql . '; [Query result served from cache]', 'clickhouse');