make isPromise() return boolean value for null and undefined cases (#6785)

* make isPromise() return boolean value for null and undefined cases
updated as per the review comments

* updated as per review comment
#6785 (comment)

* added a test

Author: Jayasankar-m

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

@@ -59,8 +59,23 @@ describe('promise', function () {
     }
   })
 
-  const _assertIsPromise = (p) => assert.ok(promise.isPromise(p))
-  const _assertNotPromise = (v) => assert.ok(!promise.isPromise(v))
+  it('isPromise', () => {
+    const v = () => {};
+    const x = new Promise(v, v);
+    const p = createRejectedPromise('reject');
+    const q = Promise.resolve("resolved");
+    assert.equal(true, promise.isPromise(x));
+    assert.equal(true, promise.isPromise(p));
+    assert.equal(true, promise.isPromise(q));
+    assert.equal(false, promise.isPromise(0));
+    assert.equal(false, promise.isPromise(false));
+    assert.equal(false, promise.isPromise(true));
+    assert.equal(false, promise.isPromise(null));
+    assert.equal(false, promise.isPromise(undefined));
+    assert.equal(false, promise.isPromise(''));
+    assert.equal(false, promise.isPromise('promise'));
+    assert.equal(false, promise.isPromise(v));
+  });
 
   function defer() {
     let d = {}