Revert "refactor(LocalStorageObjectProvider): use getItem() and setItem()"

This reverts commit 4f8403adab.

src/plugins/localStorage/LocalStorageObjectProvider.js

@@ -71,14 +71,14 @@ export default class LocalStorageObjectProvider {
    * @private
    */
   persistSpace(space) {
-    this.localStorage.setItem(this.spaceKey, JSON.stringify(space));
+    this.localStorage[this.spaceKey] = JSON.stringify(space);
   }
 
   /**
    * @private
    */
   getSpace() {
-    return this.localStorage.getItem(this.spaceKey);
+    return this.localStorage[this.spaceKey];
   }
 
   /**
@@ -93,7 +93,7 @@ export default class LocalStorageObjectProvider {
    */
   initializeSpace() {
     if (this.isEmpty()) {
-      this.localStorage.setItem(this.spaceKey, JSON.stringify({}));
+      this.localStorage[this.spaceKey] = JSON.stringify({});
     }
   }
 
@@ -101,6 +101,6 @@ export default class LocalStorageObjectProvider {
    * @private
    */
   isEmpty() {
-    return this.getSpace() === null;
+    return this.getSpace() === undefined;
   }
 }