id defaults to undefined

Readme.md

@@ -46,7 +46,7 @@ The default `request` serializer. Returns and object:
 
 ```js
 {
-  id: 'string', // Default is an empty string, unless there is an `id` property 
+  id: 'string', // Defaults to `undefined`, unless there is an `id` property 
                 // already attached to the `request` object or to the `request.info`
                 // object. Attach a synchronous function
                 // to the `request.id` that returns an identifier to have

lib/req.js

@@ -56,7 +56,7 @@ function reqSerializer (req) {
   var connection = req.connection
   const _req = Object.create(pinoReqProto)
   // req.info is for hapi compat.
-  _req.id = (typeof req.id === 'function' ? req.id() : (req.id || (req.info && req.info.id))) || ''
+  _req.id = (typeof req.id === 'function' ? req.id() : (req.id || (req.info ? req.info.id : undefined)))
   _req.method = req.method
   // req.url.path is  for hapi compat.
   _req.url = req.url ? (req.url.path || req.url) : undefined

test/req.test.js

@@ -83,6 +83,24 @@ test('req.raw will be obtained in from input request raw property if input reque
   }
 })
 
+test('req.id defaults to undefined', function (t) {
+  t.plan(1)
+
+  var server = http.createServer(handler)
+  server.unref()
+  server.listen(0, () => {
+    http.get(server.address(), () => {})
+  })
+
+  t.tearDown(() => server.close())
+
+  function handler (req, res) {
+    var serialized = serializers.reqSerializer(req)
+    t.is(serialized.id, undefined)
+    res.end()
+  }
+})
+
 test('req.id has a non-function value', function (t) {
   t.plan(1)