child_process: properly support optional args

Currently, a TypeError is incorrectly thrown if the second argument is
an object. This commit allows the args argument to be properly omitted.

Fixes: #6068
Reviewed-by: Trevor Norris <trev.norris@gmail.com>

lib/child_process.js

@@ -711,7 +711,7 @@ var spawn = exports.spawn = function(file /*, args, options*/) {
   if (Array.isArray(arguments[1])) {
     args = arguments[1].slice(0);
     options = arguments[2];
-  } else if (arguments[1] && !Array.isArray(arguments[1])) {
+  } else if (arguments[1] && typeof arguments[1] !== 'object') {
     throw new TypeError('Incorrect value of args option');
   } else {
     args = [];

test/simple/test-child-process-spawn-typeerror.js

@@ -22,12 +22,13 @@
 var spawn = require('child_process').spawn,
   assert = require('assert'),
   windows = (process.platform === 'win32'),
-  cmd = (windows) ? 'ls' : 'dir',
+  cmd = (windows) ? 'dir' : 'ls',
+  invalidcmd = (windows) ? 'ls' : 'dir',
   errors = 0;
 
 try {
   // Ensure this throws a TypeError
-  var child = spawn(cmd, 'this is not an array');
+  var child = spawn(invalidcmd, 'this is not an array');
 
   child.on('error', function (err) {
     errors++;
@@ -37,6 +38,11 @@ try {
   assert.equal(e instanceof TypeError, true);
 }
 
+// verify that args argument is optional
+assert.doesNotThrow(function() {
+  spawn(cmd, {});
+});
+
 process.on('exit', function() {
   assert.equal(errors, 0);
 });