key lookup when not in root context with undefined/null value fails,

fixes janl#397, fixes janl#409

mustache.js

@@ -334,7 +334,7 @@
    * maintaining a reference to the parent context.
    */
   function Context(view, parentContext) {
-    this.view = view == null ? {} : view;
+    this.view = view;
     this.cache = { '.': this.view };
     this.parent = parentContext;
   }
@@ -368,11 +368,16 @@
 
           while (value != null && index < names.length)
             value = value[names[index++]];
-        } else if (typeof context.view == 'object') {
+        } else if (context.view != null && typeof context.view === 'object') {
           value = context.view[name];
         }
 
-        if (value != null)
+        // TO-DO: auxiliar function instead of this beautiful if
+        if (value !== undefined ||
+          (value === undefined &&
+            (context.view === undefined) || (
+              typeof context.view === 'object' &&
+              context.view.hasOwnProperty(name))))
           break;
 
         context = context.parent;

test/_files/falsy_array.js

@@ -0,0 +1,10 @@
+({
+  "list": [
+  	["", "emptyString"],
+  	[[], "emptyArray"],
+  	[0, "zero"],
+  	[null, "null"],
+  	[undefined, "undefined"],
+  	[0/0, "NaN"]
+  ]
+})

test/_files/falsy_array.mustache

@@ -0,0 +1,3 @@
+{{#list}}
+{{#.}}{{#.}}{{.}}{{/.}}{{^.}}inverted {{/.}}{{/.}}
+{{/list}}

test/_files/falsy_array.txt

@@ -0,0 +1,6 @@
+inverted emptyString
+inverted emptyArray
+inverted zero
+inverted null
+inverted undefined
+inverted NaN

test/_files/null_lookup_array.js

@@ -0,0 +1,9 @@
+({
+    "name": "David",
+    "twitter": "@dasilvacontin",
+    "farray": [
+    	["Flor", "@florrts"],
+    	["Miquel", null],
+    	["Chris", undefined]
+    ]
+})

test/_files/null_lookup_array.mustache

@@ -0,0 +1,3 @@
+{{#farray}}
+{{#.}}{{#.}}{{.}} {{/.}}{{^.}}no twitter{{/.}}{{/.}}
+{{/farray}}

test/_files/null_lookup_array.txt

@@ -0,0 +1,3 @@
+Flor @florrts 
+Miquel no twitter
+Chris no twitter

test/_files/null_lookup_object.js

@@ -0,0 +1,18 @@
+({
+    "name": "David",
+    "twitter": "@dasilvacontin",
+    "fobject": [
+    	{
+    		"name": "Flor",
+    		"twitter": "@florrts"
+    	},
+    	{
+	        "name": "Miquel",
+	        "twitter": null
+	    },
+	    {
+	    	"name": "Chris",
+	        "twitter": undefined
+	    }
+    ]
+})

test/_files/null_lookup_object.mustache

@@ -0,0 +1,3 @@
+{{#fobject}}
+{{name}}'s twitter: {{#twitter}}{{.}}{{/twitter}}{{^twitter}}unknown{{/twitter}}.
+{{/fobject}}

test/_files/null_lookup_object.txt

@@ -0,0 +1,3 @@
+Flor's twitter: @florrts.
+Miquel's twitter: unknown.
+Chris's twitter: unknown.