Add undefined and null literal support

This adds the UndefinedLiteral and NullLiteral to AST.

Fixes #990

spec/basic.js

@@ -66,6 +66,16 @@ describe("basic context", function() {
     shouldCompileTo('val: {{{val1/val2}}}', {val1: {val2: false}}, 'val: false');
   });
 
+  it('should handle undefined and null', function() {
+    shouldCompileTo('{{awesome undefined null}}',
+        {
+          awesome: function(_undefined, _null, options) {
+            return (_undefined === undefined) + ' ' + (_null === null) + ' ' + (typeof options);
+          }
+        },
+        'true true object');
+  });
+
   it("newlines", function() {
       shouldCompileTo("Alan's\nTest", {}, "Alan's\nTest");
       shouldCompileTo("Alan's\rTest", {}, "Alan's\rTest");

spec/javascript-compiler.js

@@ -23,7 +23,7 @@ describe('javascript-compiler api', function() {
     // Tests nameLookup dot vs. bracket behavior.  Bracket is required in certain cases
     // to avoid errors in older browsers.
     it('should handle reserved words', function() {
-      shouldCompileTo("{{foo}} {{~null~}}", { foo: "food" }, "food");
+      shouldCompileTo("{{foo}} {{~[null]~}}", { foo: "food" }, "food");
     });
   });
   describe('#compilerInfo', function() {

spec/parser.js

@@ -58,6 +58,10 @@ describe('parser', function() {
     equals(ast_for("{{foo false}}"), "{{ PATH:foo [BOOLEAN{false}] }}\n");
   });
 
+  it('parses mustaches with undefined and null parameters', function() {
+    equals(ast_for("{{foo undefined null}}"), "{{ PATH:foo [UNDEFINED, NULL] }}\n");
+  });
+
   it('parses mutaches with DATA parameters', function() {
     equals(ast_for("{{foo @bar}}"), "{{ PATH:foo [@PATH:bar] }}\n");
   });

spec/tokenizer.js

@@ -322,6 +322,13 @@ describe('Tokenizer', function() {
     shouldBeToken(result[2], "BOOLEAN", "false");
   });
 
+  it('tokenizes undefined and null', function() {
+    var result = tokenize('{{ foo undefined null }}');
+    shouldMatchTokens(result, ['OPEN', 'ID', 'UNDEFINED', 'NULL', 'CLOSE']);
+    shouldBeToken(result[2], 'UNDEFINED', 'undefined');
+    shouldBeToken(result[3], 'NULL', 'null');
+  });
+
   it('tokenizes hash arguments', function() {
     var result = tokenize("{{ foo bar=baz }}");
     shouldMatchTokens(result, ['OPEN', 'ID', 'ID', 'EQUALS', 'ID', 'CLOSE']);

spec/visitor.js

@@ -9,7 +9,7 @@ describe('Visitor', function() {
     // Simply run the thing and make sure it does not fail and that all of the
     // stub methods are executed
     var visitor = new Handlebars.Visitor();
-    visitor.accept(Handlebars.parse('{{foo}}{{#foo (bar 1 "1" true) foo=@data}}{{!comment}}{{> bar }} {{/foo}}'));
+    visitor.accept(Handlebars.parse('{{foo}}{{#foo (bar 1 "1" true undefined null) foo=@data}}{{!comment}}{{> bar }} {{/foo}}'));
   });
 
   it('should traverse to stubs', function() {