Fix [object Object] errors

Fixes #322
Fixes #330
Fixes #331
Fixes #334

mustache.js

@@ -121,7 +121,7 @@
   };
 
   function Context(view, parent) {
-    this.view = view || {};
+    this.view = view == null ? {} : view;
     this.parent = parent;
     this._cache = {};
   }
@@ -135,9 +135,10 @@
   };
 
   Context.prototype.lookup = function (name) {
-    var value = this._cache[name];
-
-    if (!value) {
+    var value;
+    if (name in this._cache) {
+      value = this._cache[name];
+    } else {
       if (name === '.') {
         value = this.view;
       } else {
@@ -148,7 +149,7 @@
             value = context.view;
 
             var names = name.split('.'), i = 0;
-            while (value && i < names.length) {
+            while (value != null && i < names.length) {
               value = value[names[i++]];
             }
           } else {

test/_files/zero_view.js

@@ -0,0 +1 @@
+({ nums: [0, 1, 2] })

test/_files/zero_view.mustache

@@ -0,0 +1 @@
+{{#nums}}{{.}},{{/nums}}

test/_files/zero_view.txt

@@ -0,0 +1 @@
+0,1,2,

test/context-test.js

@@ -43,6 +43,23 @@ describe('A new Mustache.Context', function () {
   });
 });
 
+describe('A Mustache.Context', function () {
+  var context;
+
+  describe('with an empty string in the lookup chain', function () {
+    var view, context;
+    beforeEach(function () {
+      view = { a: '' };
+      view.a.b = 'value';
+      context = new Context(view);
+    });
+
+    it('is able to lookup a nested property', function () {
+      assert.equal(context.lookup('a.b'), view.a.b);
+    });
+  });
+});
+
 describe('Mustache.Context.make', function () {
   it('returns the same object when given a Context', function () {
     var context = new Context;