util: make _extend() more robust

Add a better 'is object?' check, the old one let values like true slip through.

lib/util.js

@@ -509,7 +509,7 @@ exports.inherits = function(ctor, superCtor) {
 
 exports._extend = function(origin, add) {
   // Don't do anything if add isn't an object
-  if (!add) return origin;
+  if (!add || typeof add !== 'object') return origin;
 
   var keys = Object.keys(add);
   var i = keys.length;

test/simple/test-util.js

@@ -69,3 +69,12 @@ assert.equal(false, util.isError({}));
 assert.equal(false, util.isError({ name: 'Error', message: '' }));
 assert.equal(false, util.isError([]));
 assert.equal(false, util.isError(Object.create(Error.prototype)));
+
+// _extend
+assert.deepEqual(util._extend({a:1}),             {a:1});
+assert.deepEqual(util._extend({a:1}, []),         {a:1});
+assert.deepEqual(util._extend({a:1}, null),       {a:1});
+assert.deepEqual(util._extend({a:1}, true),       {a:1});
+assert.deepEqual(util._extend({a:1}, false),      {a:1});
+assert.deepEqual(util._extend({a:1}, {b:2}),      {a:1, b:2});
+assert.deepEqual(util._extend({a:1, b:2}, {b:3}), {a:1, b:3});