Upgrades dependencies, adds strict null checks

Author: philipstanislaus

build/arrayToTree.d.ts

@@ -4,7 +4,7 @@ export interface Item {
     [key: string]: any;
 }
 export interface TreeItem {
-    data: Item;
+    data: Item | null;
     children: TreeItem[];
 }
 export interface Config {

package.json

@@ -9,18 +9,18 @@
   "license": "MIT",
   "dependencies": {},
   "devDependencies": {
-    "@types/chai": "^3.5.2",
+    "@types/chai": "^4.0.4",
     "@types/mocha": "^2.2.41",
-    "chai": "^3.5.0",
+    "chai": "^4.1.2",
     "coveralls": "^2.13.1",
     "istanbul": "^0.4.5",
     "mocha": "^3.3.0",
     "mocha-lcov-reporter": "^1.3.0",
     "remap-istanbul": "^0.9.5",
     "tslint": "^5.2.0",
-    "tslint-config-standard": "^5.0.2",
+    "tslint-config-standard": "^6.0.1",
     "typescript": "^2.3.2",
-    "uglify-js": "^2.8.23"
+    "uglify-js": "^3.1.1"
   },
   "scripts": {
     "preversion": "yarn && npm run lint && npm run build && npm run test-and-send-cov-to-coveralls",

src/arrayToTree.ts

@@ -5,7 +5,7 @@ export interface Item {
 }
 
 export interface TreeItem {
-  data: Item
+  data: Item|null
   children: TreeItem[]
 }
 

tsconfig.json

@@ -6,7 +6,8 @@
     "sourceMap": true,
     "moduleResolution": "node",
     "outDir": "build",
-    "declaration": true
+    "declaration": true,
+    "strictNullChecks": true
   },
   "exclude": [
     "node_modules",