CacheStaticName data returning empty in fetch event

This is my sw.js
```
const staticDevCoffee = "dev-coffee-site-v1";
const dynamicCacheName = "dev-coffee-dynamic-v4";
const assets = [
"/",
"/index.html",
"/fallback.html",
"/about.html",
"/contact.html",
"/blog.html",
"/css/style.css",
"/js/app.js",
"/images/coffee1.jpg",
"/images/coffee2.jpg",
"/images/coffee3.jpg",
"/images/coffee4.jpg",
"/images/coffee5.jpg",
"/images/coffee6.jpg",
"/images/coffee7.jpg",
"/images/coffee8.jpg",
"/images/coffee9.jpg",
]
self.addEventListener("install", installEvent => {
installEvent.waitUntil(
caches.open(staticDevCoffee).then(cache => {
cache.addAll(assets)
})
);
});
self.addEventListener('activate', activateEvent => {
activateEvent.waitUntil(
caches.keys().then(keys => {
return Promise.all(keys
.filter(key => key !== staticDevCoffee && key !== dynamicCacheName)
.map(key => caches.delete(key))
);
})
);
});

self.addEventListener('fetch', fetchEvent => {
if(!(fetchEvent.request.url.indexOf("http") === 0)) return
fetchEvent.respondWith(
caches.match(fetchEvent.request).then(cacheRes => {
return cacheRes || fetch(fetchEvent.request).then(fetchRes => {
return caches.open(staticDevCoffee).then(cache => {
cache.put(fetchEvent.request.url, fetchRes.clone());
return fetchRes;
})
});
}).catch(()=> caches.match("/fallback.html"))
);
});
```
After adding cache delete method in fetch method sw returning staticCacheName but empty