strict null check

tsconfig.json

@@ -1,9 +1,9 @@
 {
   "compileOnSave": true,
   "compilerOptions": {
-    "target": "es6",
+    "target": "es5",
     "moduleResolution": "node",
-    "strictNullChecks": false,
+    "strictNullChecks": true,
     "alwaysStrict": true,
     "sourceMap": true,
     "declaration": true,