Add NullCacheAdapter (#2636)

* Add NullCacheAdapter

* clear returns promise explicitly

* Add NullCacheAdapter accessor

src/Adapters/Cache/NullCacheAdapter.js

@@ -0,0 +1,25 @@
+export class NullCacheAdapter {
+
+  constructor(ctx) {
+  }
+
+  get(key) {
+    return new Promise((resolve, _) => {
+      return resolve(null);
+    })
+  }
+
+  put(key, value, ttl) {
+    return Promise.resolve();
+  }
+
+  del(key) {
+    return Promise.resolve();
+  }
+
+  clear() {
+    return Promise.resolve();
+  }
+}
+
+export default NullCacheAdapter;