bunyan: Potentially fix logging error properties

lib/bunyan.mjs

@@ -771,13 +771,19 @@ Logger.prototype._emit = function (rec, noemit) {
 function mkRecord(log, minLevel, args) {
   var excludeFields, fields, msgArgs;
   if (args[0] instanceof Error) {
+    var err = args[0];
     // `log.<level>(err, ...)`
     fields = {
       // Use this Logger's err serializer, if defined.
       err: (log.serializers && log.serializers.err
-        ? log.serializers.err(args[0])
-        : Logger.stdSerializers.err(args[0]))
+        ? log.serializers.err(err)
+        : Logger.stdSerializers.err(err))
     };
+    for (const key in err) {
+      if (Object.prototype.hasOwnProperty.call(err, key)) {
+          fields[key] = err[key];
+      }
+    }
     excludeFields = {err: true};
     if (args.length === 1) {
       msgArgs = [fields.err.message];

package.json

@@ -1,6 +1,6 @@
 {
   "name": "bunyan-lite",
-  "version": "1.2.0",
+  "version": "1.2.1",
   "description": "a lite version of bunyan, a JSON logging library for node.js services with zero dependency",
   "author": "Jonatan Nilsson <jonatan@nilsson.is> (https://nfp.is)",
   "main": "./lib/bunyan.mjs",