Fixed empty string not being returned.

This closes #59.

Author: rmariuzzo

src/lang.js

@@ -284,7 +284,7 @@
         var subKey = '';
         while (entries.length && message !== undefined) {
             var subKey = !subKey ? entries.shift() : subKey.concat('.', entries.shift());
-            if (message[subKey]) {
+            if (message[subKey] !== undefined) {
                 message = message[subKey]
                 subKey = '';
             }

test/fixture/messages.json

@@ -114,7 +114,8 @@
         },
         "dotInKey": {
             "dot.in.key": "Dot In Key Nested Simple"
-        }
+        },
+        "empty": ""
     },
     "en.pagination": {
         "previous": "« Previous",

test/spec/lang_get_spec.js

@@ -73,4 +73,8 @@ describe('The lang.get() method', function () {
         expect(lang.get('messages.dotInKey.dot.in.key')).toBe('Dot In Key Nested Simple');
         expect(lang.get('messages.dot.in.key2.nested.dot.in.key2.nested')).toBe('Dot In Key Nested Tricky');
     });
+
+    it('should return an empty string', function() {
+        expect(lang.get('messages.empty')).toBe('');
+    })
 });