fix: support null valued config attributes

src/utils/helpers.ts

@@ -2,7 +2,7 @@ export function deepFreeze<T>(obj: T): void {
   const propNames = Object.getOwnPropertyNames(obj);
   for (const name of propNames) {
     const value = obj[name as keyof T];
-    if (typeof value === 'object') {
+    if (typeof value === 'object' && value !== null) {
       deepFreeze(value);
     }
   }

tests/helpers.spec.ts

@@ -0,0 +1,35 @@
+import { deepFreeze } from '../src/utils/helpers';
+
+describe('helpers', () => {
+  describe('#deepFreeze', () => {
+    it('should return object freeze', () => {
+      const data = {
+        name: 'I am parent',
+        child: {
+          name: 'I am child',
+        },
+      };
+      deepFreeze(data);
+
+      const action = () => {
+        data.name = 'i try to change'; // try to change freezed object
+      };
+      expect(action).toThrow(/Cannot assign to read only property/);
+    });
+
+    it('should return object freeze with null value', () => {
+      const data = {
+        name: 'I am parent',
+        child: {
+          name: null,
+        },
+      };
+      deepFreeze(data);
+
+      const action = () => {
+        data.name = 'i try to change'; // try to change freezed object
+      };
+      expect(action).toThrow(/Cannot assign to read only property/);
+    });
+  });
+});