fix($parse): treat falsy values as defined in assignment expressions

Closes #14990

Author: m-amr

src/ng/parse.js

@@ -1042,7 +1042,7 @@ ASTCompiler.prototype = {
           self.if_(self.stage === 'inputs' || 's', function() {
             if (create && create !== 1) {
               self.if_(
-                self.not(self.nonComputedMember('s', ast.name)),
+                self.isNull(self.nonComputedMember('s', ast.name)),
                 self.lazyAssign(self.nonComputedMember('s', ast.name), '{}'));
             }
             self.assign(intoId, self.nonComputedMember('s', ast.name));
@@ -1079,7 +1079,7 @@ ASTCompiler.prototype = {
           } else {
             ensureSafeMemberName(ast.property.name);
             if (create && create !== 1) {
-              self.if_(self.not(self.nonComputedMember(left, ast.property.name)), self.lazyAssign(self.nonComputedMember(left, ast.property.name), '{}'));
+              self.if_(self.isNull(self.nonComputedMember(left, ast.property.name)), self.lazyAssign(self.nonComputedMember(left, ast.property.name), '{}'));
             }
             expression = self.nonComputedMember(left, ast.property.name);
             if (self.state.expensiveChecks || isPossiblyDangerousMemberName(ast.property.name)) {
@@ -1274,6 +1274,10 @@ ASTCompiler.prototype = {
     return '!(' + expression + ')';
   },
 
+  isNull: function(expression) {
+    return expression + '==null';
+  },
+
   notNull: function(expression) {
     return expression + '!=null';
   },

test/ng/parseSpec.js

@@ -3900,6 +3900,34 @@ describe('parser', function() {
           expect(isFunction(s.toString)).toBe(true);
           expect(l.toString).toBe(1);
         }));
+
+        it('should assign a property to locals properties with null or undefined value', inject(function($parse) {
+          var local = {a:null};
+          $parse("a.b =1")(local);
+          expect(local.a).toEqual({b:1});
+
+          local.a = undefined;
+          $parse("a.b =1")(local);
+          expect(local.a).toEqual({b:1});
+        }));
+
+        it('should not assign a property to locals properties with falsy value', inject(function($parse) {
+          var local = {a:0};
+
+          expect(function() {
+            $parse("a.b =1")(local);
+          }).toThrow();
+
+          local.a = false;
+          expect(function() {
+            $parse("a.b =1")(local);
+          }).toThrow();
+
+          local.a = '';
+          expect(function() {
+            $parse("a.b =1")(local);
+          }).toThrow();
+        }));
       });
 
       describe('literal', function() {