When compiling templates that use string concatenation, treat null and undefined as empty strings so that the the literal "null" and "undefined" don't get written

compiler/TemplateBuilder.js

@@ -250,9 +250,12 @@ function TemplateBuilder(compiler, path, rootNode) {
     this.helperFunctionsAdded = {};
     this.vars = [];
     this.varsLookup = {};
+
+    this.getStaticHelperFunction('toString', 's');
     this.getStaticHelperFunction('empty', 'e');
     this.getStaticHelperFunction('notEmpty', 'ne');
 }
+
 TemplateBuilder.prototype = {
 
     captureCode: function (func, thisObj) {
@@ -283,7 +286,7 @@ TemplateBuilder.prototype = {
     addStaticVar: function (name, expression) {
         name = safeVarName(name);
         
-        if (!this.staticVarsLookup[name]) {
+        if (!this.staticVarsLookup.hasOwnProperty(name)) {
             this.staticVarsLookup[name] = true;
             this.staticVars.push({
                 name: name,

compiler/expression-parser.js

@@ -238,7 +238,7 @@ ExpressionParserHelper.prototype = {
                 // We don't need to surround with parentheses if
                 // the expression will be escaped since the expression
                 // is an argument to a function call
-                expression = '(' + expression + ')';
+                expression = 'toString(' + expression + ')';
             }
             expression = new Expression(expression);
         }

runtime/helpers.js

@@ -14,6 +14,10 @@ function notEmpty(o) {
 }
 
 module.exports = {
+    s: function(str) {
+        return (str == null) ? '' : str;
+    },
+
     fv: function (array, callback) {
         if (!array) {
             return;