chore(ts): add strict null checks

Author: steabert

tsconfig.json

@@ -2,7 +2,7 @@
   "compilerOptions": {
     /* Include Typescript declaration files */
     "declaration": true,
-    
+
     /* Basic Options */
     "target": "es2015",
     "module": "es2015",
@@ -13,6 +13,7 @@
 
     /* Strict Type-Checking Options */
     "strict": true,
+    "strictNullChecks": true,
 
     /* Module Resolution Options */
     "moduleResolution": "node",