feat(parser): change Parser to return null when one of the operands is null

modules/change_detection/src/parser/ast.js

@@ -86,19 +86,7 @@ export class Binary extends AST {
     var right = this.right.eval(context, formatters);
 
     // Null check for the operations.
-    if (left == null || right == null) {
-      switch (this.operation) {
-        case '+':
-          if (left != null) return left;
-          if (right != null) return right;
-          return 0;
-        case '-':
-          if (left != null) return left;
-          if (right != null) return 0 - right;
-          return 0;
-      }
-      return null;
-    }
+    if (left == null || right == null) return null;
 
     switch (this.operation) {
       case '+'  : return autoConvertAdd(left, right);

modules/change_detection/test/parser/parser_spec.js

@@ -18,6 +18,10 @@ export function main() {
   var context = td();
   var formatters;
 
+  function createParser() {
+    return new Parser(new Lexer(), new ClosureMap());
+  }
+
   function _eval(text) {
     return new Parser(new Lexer(), new ClosureMap()).parse(text)
       .eval(context, formatters);
@@ -36,7 +40,7 @@ export function main() {
       var parser;
 
       beforeEach(() => {
-        parser = new Parser(new Lexer(), new ClosureMap());
+        parser = createParser();
       });
 
       it("should parse field access",() => {
@@ -119,6 +123,22 @@ export function main() {
         expectEval("4 + 4 + ' str'").toEqual("8 str");
         expectEval("'str ' + 4 + 4").toEqual("str 44");
       });
+
+      it('should behave gracefully with a null scope', () => {
+        var exp = createParser().parse("null");
+        expect(exp.eval(null, null)).toEqual(null);
+      });
+
+      it('should eval binary operators with null as null', () => {
+        expectEval("null < 0").toBeNull();
+        expectEval("null * 3").toBeNull();
+        expectEval("null + 6").toBeNull();
+        expectEval("5 + null").toBeNull();
+        expectEval("null - 4").toBeNull();
+        expectEval("3 - null").toBeNull();
+        expectEval("null + null").toBeNull();
+        expectEval("null - null").toBeNull();
+      });
     });
     
     describe("error handling", () => {