render undefined to ''

README.md

@@ -102,9 +102,7 @@ Footer
 * It's possible to define multiple blocks.
 * block name is optional when there's only one block.
 
-## Extension
-
-Register Filters:
+## Register Filters
 
 ```javascript
 // Usage: {{ name | uppper }}
@@ -115,7 +113,7 @@ engine.registerFilter('upper', function(v){
 
 > See existing filter implementations: <https://github.com/harttle/shopify-liquid/blob/master/filters.js>
 
-Register Tags:
+## Register Tags
 
 ```javascript
 // Usage: {% upper name%}

package.json

@@ -1,6 +1,6 @@
 {
   "name": "shopify-liquid",
-  "version": "1.1.7",
+  "version": "1.1.8",
   "description": "A Shopify Liquid Implementation in Node.js",
   "main": "index.js",
   "scripts": {

src/render.js

@@ -21,7 +21,7 @@ var render = {
                     break;
                 case 'output':
                     var val = this.evalOutput(template, scope);
-                    html += stringify(val);
+                    html += val === undefined ? '' : stringify(val);
             }
         });
         return html;

test/liquid.js

@@ -32,6 +32,9 @@ describe('liquid', function() {
     it('should output array', function() {
         engine.parseAndRender('{{arr}}', ctx).should.equal('[-2,"a"]');
     });
+    it('should output undefined to empty', function() {
+        engine.parseAndRender('foo{{zzz}}bar', ctx).should.equal('foobar');
+    });
     it('should parse html', function() {
         (function() {
             engine.parse('{{obj}}');