[js] fix capabilities serialize

Closes #1950

Signed-off-by: Jason Leyba <jmleyba@gmail.com>

javascript/node/selenium-webdriver/CHANGES.md

@@ -5,6 +5,8 @@
 * Deprecated `Promise#thenFinally()` - use `Promise#finally()`. The thenFinally
    shim added to the promise module in v2.53.0 will be removed in v3.0
    Sorry for the churn!
+* FIXED: capabilities serialization now properly handles undefined vs.
+   false-like values.
 
 ## v2.53.1
 

javascript/node/selenium-webdriver/lib/capabilities.js

@@ -431,7 +431,7 @@ function serialize(caps) {
   let ret = {};
   for (let key of caps.keys()) {
     let cap = caps.get(key);
-    if (cap) {
+    if (cap !== undefined && cap !== null) {
       ret[key] = cap;
     }
   }

javascript/node/selenium-webdriver/test/lib/capabilities_test.js

@@ -76,9 +76,36 @@ describe('Capabilities', function() {
     assert.equal('def', caps.get('abc'));
   });
 
-  it('can be serialized', function() {
-    let m = new Map([['one', 123], ['abc', 'def']]);
-    let caps = new Capabilities(m);
-    assert.deepEqual({one: 123, abc: 'def'}, caps[Symbols.serialize]());
+  describe('serialize', function() {
+    it('works for simple capabilities', function() {
+      let m = new Map([['one', 123], ['abc', 'def']]);
+      let caps = new Capabilities(m);
+      assert.deepEqual({one: 123, abc: 'def'}, caps[Symbols.serialize]());
+    });
+
+    it('does not omit capabilities set to a false-like value', function() {
+      let caps = new Capabilities;
+      caps.set('bool', false);
+      caps.set('number', 0);
+      caps.set('string', '');
+
+      assert.deepEqual(
+          {bool: false, number: 0, string: ''},
+          caps[Symbols.serialize]());
+    });
+
+    it('omits capabilities with a null value', function() {
+      let caps = new Capabilities;
+      caps.set('foo', null);
+      caps.set('bar', 123);
+      assert.deepEqual({bar: 123}, caps[Symbols.serialize]());
+    });
+
+    it('omits capabilities with an undefined value', function() {
+      let caps = new Capabilities;
+      caps.set('foo', undefined);
+      caps.set('bar', 123);
+      assert.deepEqual({bar: 123}, caps[Symbols.serialize]());
+    });
   });
 });