fix: 🐛 Ensure undefined is not serialzed (#21)

* fix: 🐛 Ensure undefined is not serialzed

Prior to this change, messages that 'undefined' are attempted to
be serialized - this would cause the following exception to be
raised:

```bash
TypeError: Cannot read properties of undefined (reading 'type')
```

After this change, a simple non-null assertion is made to ensure
the type of the value is not accessed if the value is undefined

* refactor: ♻️  Return early if falsy

* Update src/serializers/JSONSerializer/index.ts

Co-authored-by: Peter McIntyre <[email protected]>

---------

Co-authored-by: Peter McIntyre <[email protected]>

src/serializers/JSONSerializer/index.test.ts

@@ -9,11 +9,20 @@ describe(`when serializing errors`, () => {
 
 describe(`when serializing buffers`, () => {
     test('should stringify the buffer', () => {
-        const got =  JSONSerializer({ word: Buffer.from('example') })
+        const got = JSONSerializer({ word: Buffer.from('example') })
         expect(got).toEqual(`{"word":"example"}`)
     })
 })
 
+describe(`when serializing undefined or null objects`, () => {
+    test.each([
+        [undefined, undefined],
+        [null, 'null'],
+    ])('should not attempt to serialize', (input, expected) => {
+        expect(JSONSerializer(input)).toEqual(expected)
+    })
+})
+
 // more info
 // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Cyclic_object_value
 describe(`when serializing recursive objects`, () => {

src/serializers/JSONSerializer/index.ts

@@ -19,14 +19,14 @@ function getCircularReplacer() {
 
 // toStringers strigifies some specific types
 function toStringers(_: any, value: any) {
+    // exit early for null and undefined
+    if (value === undefined || value === null) return value
 
     // error
-    if (value instanceof Error)
-        return value.toString()
+    if (value instanceof Error) return value.toString()
 
     // buffer
-    if (value.type !== undefined && value.type === "Buffer")
-        return Buffer.from(value).toString()
+    if (value.type === 'Buffer') return Buffer.from(value).toString()
 
     return value
 }