diff --git a/lib/middleware/cache.js b/lib/middleware/cache.js
index 487793766..a764b0fdd 100644
--- a/lib/middleware/cache.js
+++ b/lib/middleware/cache.js
@@ -36,11 +36,12 @@ module.exports = function(app, options = {}) {
         app.context.cache = {
             get: async (key) => {
                 if (key) {
-                    const value = await redisClient.get(key);
+                    let value = await redisClient.get(key);
                     if (value) {
                         await redisClient.expire(key, 24 * 60 * 60);
+                        value = value + '';
                     }
-                    return value + '';
+                    return value;
                 }
             },
             set: async function(key, value, maxAge = 24 * 60 * 60) {
@@ -81,7 +82,11 @@ module.exports = function(app, options = {}) {
         app.context.cache = {
             get: (key) => {
                 if (key) {
-                    return routeCache.get(key) + '';
+                    let value = routeCache.get(key);
+                    if (value) {
+                        value = value + '';
+                    }
+                    return value;
                 }
             },
             set: (key, value, maxAge = 24 * 60 * 60) => {