Fix error when unset user email

spec/ParseUser.spec.js

@@ -1834,6 +1834,22 @@ describe('Parse.User testing', () => {
     });
   });
 
+  it('unset user email', (done) => {
+    var user = new Parse.User();
+    user.set('username', 'test');
+    user.set('password', 'test');
+    user.set('email', 'test@test.com');
+    user.signUp().then(() => {
+      user.unset('email');
+      return user.save();
+    }).then(() => {
+      done();
+    }, (error) => {
+      fail('Should not fail');
+      done();
+    });
+  });
+
   it('create session from user', (done) => {
     Parse.Promise.as().then(() => {
       return Parse.User.signUp("finn", "human", { foo: "bar" });

src/RestWrite.js

@@ -356,7 +356,7 @@ RestWrite.prototype.transformUser = function() {
         return Promise.resolve();
       });
   }).then(() => {
-    if (!this.data.email) {
+    if (!this.data.email || this.data.email.__op === 'Delete') {
       return;
     }
     // Validate basic email address format